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I usually run 'w' first when troubleshooting unknown machines (rachelbythebay.com)
685 points by weinzierl 9 months ago | hide | past | web | favorite | 243 comments

I too instinctively run `w` whenever I log into a machine, and that instinct helped me land my current job.

One hour long component of a (now deprecated) SRE interview loop was for the candidate to SSH into a series of EC2 instances and debug issues which got progressively harder as the interview wore on.

I had wasted a substantial amount of time on the first and easiest problem by really overthinking it, and not trying the simplest of debugging techniques first. By the time I got to the final, hardest problem, I had just over 5 minutes remaining. The interviewer gave me a pass to skip it, but I was having fun, and really wanted to take a crack at it.

The final problem was to try to figure out why logging into a particular machine with SSH was slow. While I sat waiting for a prompt, I had a number of thoughts. Is a reverse DNS lookup timing out? Is there a huge i/o load on the machine? Am I going to have to wire up strace to `sshd` and log in again?

When I finally get to a shell prompt, I instinctively run `w` and it just hangs. I hit ^C, `strace` it, and discover that it's blocking on:

    fcntl64(5, F_SETLKW, {type=F_RDLCK, whence=SEEK_SET, start=0, len=0}) ...
I look up a bit, and discover that file descriptor 5 is /var/run/utmp. So `w` is trying to get an advisory lock on utmp and failing. Then it hits me, `sshd` is likely also trying to acquire a lock on utmp, failing, and then eventually timing out.

A little bit later, I've found and killed the the rogue program that held the lock, and SSH logins were fast again. Solving that last problem so quickly really boosted my spirits, and gave me the energy to push through the harder interviews that came later in the day.

Thanks w!

That actually seems like a great idea for a work sample test.

In my opinion, a bit too much trivia to be a valuable indicator of SRE success. It would be really great if a candidate (who rated themselves well in systems debugging) could walk you through the strace output of a command like that.

I really like that idea. It might be fun to be given some `strace` output (with the initial `execve` and writes to stdout/stderr redacted) and then be asked to determine which UNIX command it was, or more broadly what it was doing.

How did you find the rogue program?

I would probably use lsof(8)

Or maybe fuser

Good memory and good story.

My goto for initial troubleshooting a server is:

uptime # uptime and CPU stress

w # or better yet:last |head # who is/has been in

netstat -tlpn # find server role

df -h # out of disk space?

grep kill /var/log/messages # out of memory?

ps auxf # what's running

htop # stressed? , look out for D (waiting on I/O typically) processes

history # what has changed recently

tail /var/log/application.log # anything interesting logged?

I've wasted time not checking for inode availability, so I'd add a check for that to this list:

df -hi

> w # or better yet:last |head # who is/has been in

The post argues that 'last' will not always give the desired information:

> Obviously, I could also use 'last' to see who's been on the box recently, but this isn't the whole story. It's totally possible to "ssh root@box /path/to/command" and never start a login shell, which then leaves no trace in the lastlog, but then goes on to break something on the box. The syslog is how you'd find this.

I can recommend setting up audit beat & kibana or similar. Auditbeat is a recent addition to the Elastic beats agents and it sends audit logs for a lot of things, including ssh logins, system calls, and you can monitor changes to files/directories as well. So, you can flag boxes where people are poking around in /etc, and see which boxes are being accessed via ssh by which user.

We have this and a few other elastic beats on most of our vms in amazon baked into the amis we use. So anything deployed by us starts sending lots of data to our logging cluster for metrics, auditing, internal application events, stacktraces from our docker infrastructure, syslogs, etc.

I run my own web server and email server for my law firm. I'm the only one with credentials to log in (ash), and probably the only one who would even know how to do it, and possibly the only one who knows we have servers.

And I still run w first thing almost every time out of habit.

What am I looking for? A session I accidentally left open somewhere else? Unauthorized access? A friend? Dunno...

You're leaving your firm incredible vulnerable to the "checkyoursudo gets hit by a bus" scenario aren't you? At least let the rest of your firm know you have servers and give some credentials (for another account with sudo permissions) to e.g. a managing partner or similar (with instructions to never use them unless you die).

My though exactly! For the company of checkyoursudo, he's what is called a Key Person Risk.

But in my examples, I never use the "hit-by-a-bus". Sysadmins tend to frown upon that comment.

I use the "win-the-lottery-go-to-Fiji-and-never-look-back". It always makes them smile :)

The problem with the "win-the-lottery-go-to-Fiji-and-never-look-back" as an example is it doesn't quite get the point across because they'll have time to gracefully transfer knowledge and after that they're just somewhere else in the world so I can still theoretically fly over there and beat them with a wrench until I get what I need.

Death is a real thing that really happens to people, and from an organizational perspective it is valuable to keep in mind that no one in your company is immune to that.

Yeah, it's not the same at all. I had an ex-employer that fired me multiple times, and came back to me to get forgotten passwords multiple times.

After a little soul-searching, and deciding I didn't want to harbor anger, I helped him with the ones I remembered each time.

Had I actually been hit by a bus, that wouldn't have been possible at all.

I'm sure that if I'd hit the lottery and gone to Fiji, I'd have been even more likely to help him with those passwords.

In the end, not-burning-that-bridge did help me earn more money as he hired me back several times, and I demanded more money each time until I was asking almost as much per hour as he was getting from his customers and he simply couldn't afford me.

I actually basically had this happen to me before, too. With two different employers.

Aside from one of them being super annoying, over and over again, helping them out was the right thing to do.

It's not like it cost me anything other than a couple of minutes of time.

If someone already screwed you over, then... But otherwise, why not

How do you get fired by someone multiple times?

Not learning the lesson multiple times. :)

The "hit-by-a-bus" scenario for me is expressed quite often where I work. I have no problem with it, if it is not repeaded a dozen times. Then it starts to sound like a threat..

“depart without notice and without looking back” can be just as much of a threat, though, especially if the person raising the scenario is a Key Person themselves.

Nice, and apparently you're not the only one:


"The bus factor is a measurement of the risk resulting from information and capabilities not being shared among team members, from the phrase 'in case they get hit by a bus'. It is also known as the lottery factor, ..."

I'm curious if I could get a chuckle by saying "Hit by an Uber"...

I'm laughing. Might be too early but I am.

I use "go to a vacation" as a euphemism for that.

I use "get hit by a bus" as a euphemism for vacation

A bus filled with vodka and zen

I thought it was death, getting fired, or quitting.

I guess I have worked with different types of sysadmins.

A good sysadmin has, or at least expresses traits of in their work, pessimism and realism. We have to constantly viscerally feel and know that any component can fail at any time. Remembering your own mortality goes along well with that.

Being easily disturbed by this is not a trait I would like to see in someone with these kinds of responsibilities.

So what you're saying is that Stoicism is not only a philosophy for soldiers and prisoners, but for sysadmins as well.

Yes, very well put.

I never worry about being hit buy a bus, I assume it'll be quick :-)

Reboot into single user mode, reset root password, and done.

The issue is the new admin has no way to know whether all the processes running before the reboot are configured to come up automatically, and no sense of what external dependencies the server has. Further, the admin is forced to deal with problems reactively at boot time, rather than having the opportunity to gain an understanding of the server setup in advance.

Not if grub is encrypted, better even behind FDE.

How does booting for remote login in such a setup work though? You'd have to be physically present in order to enter the passphrase.

For that I do an ssh shim at initram (with portknocking) for key entry preboot

I would love to read a tutorial on that if you know of one.

One can also assume that any competent replacement for the "checkyoursudo who was hit by a bus" is able to log into machine after a reboot.

I rather rely on beginner level sysop skills than on management understanding the implications of "this is my access to your mail server, don't handle with care, don't handle at all unless I am run over by a bus".

One way we did it at BT was all the root paswords where placed in an separate envelope per machine, and kept in the fire safe.

I do that same thing, but I have scripted it in .login ...

  echo ""
  /usr/bin/netstat -f inet | /usr/bin/grep --color -C 100 "MYHOSTNAME.ssh"
  echo ""
  echo ""
  echo ""
(note, the netstat command arguments are for FreeBSD ...)

So, when I log in, I see all current network connections, and any current SSH connections are highlighted in red.

Then double carriage return and then the output of 'w'.

You don't need the quoted empty string with echo to generate a newline, just `echo` is fine.

In case anyone didn't already figure it out, (ash) was an autocorrect error from (ssh).

Why? I'm sure it's fun for you, but it's terribly unprofessional for the lawyers to use that setup.


No. There aren't any ethics rules implicated in the way we do this.

No client files are stored on these servers.

Interesting that nobody mentioned htop so far (https://en.wikipedia.org/wiki/Htop). It is my favourite command to get a quick glance on the computational facilities of a computer (memory, cores) and what it is doing (load, fancy ps/top). htop is not installed everywhere, but it is easy to make a static build and scp it to the questioned host.

Another very handy command is

  sudo netstat -atpn
which shows you the processes and owners of open TCP/UDP ports. The argument combination is as weird as "ps aux" that I just memorized it by heart.

I remember it by imagining netstat wearing pants. There is plain ole netstat and there's netstat wearing pants.

Then there's grep -whor which is also super useful.

Thanks! I didn't knew about -o.

My most common grep phrase is grep -iIRn - good for searching in code (when IDE can't find something). You can remove -i if you care about case, but I mostly used it for plsql code, and that's not case-sensitive.

What does that do?

Pinches whole-words (by regex usually, e.g. '[A-Z][A-Za-z]*Exception') out of files recursively. Then throw in sort and uniq -c.

example? I tried a few things, clearly since -r it's not a single file grep, but throwing in -h with -r is confusing. I thought I was pretty good at grepping...

-r everyone needs, but usually -R is a better default since it does not ignore symlinks

-h I practically never use since I'm almost always using grep to find what file I need to further investigate and letting the stuff down the | line deal with it

-o makes sense, kinda, I want to do that in the next stage of the pipe, maybe I have used it once? cant remember

but -w... I feel like I'm missing something there.

I think you have dramatically different usage patterns than me. I use -o all the time. I only know -w for a limited time, but it's one of my favorite options since you can filter out a lot of garbage. You could replace it with grep -P '\bpattern\b', I guess.

I think what you are doing here is search, but -o and -w shine at data extraction and data manipulation. Things you would use Excel for, except on multiple GB files.

Very interesting. I'm still floundering for a use case... can you give an outline if it's difficult to make a specific example?

If you are not using search, but are using a recursive (-r) grep, then you are feeding a bunch of data to your pipe but don't care what file it came from. I get that... I mirrored the SEC's ftp back when it was ftp... and it's interesting for correlation and name stuff... but that's not going to work because it's freeform, and it's millions of small files... so you are using (large) files with a known format? Something like spectral datasets where the fields are passed with the data prefixed with it's important tags? Maybe logs?

As I have already said,

    grep -whor '[A-Z][A-Za-z]*Exception' * | sort | uniq -c
for a histogram of exceptions inside logs downloaded from a bunch of nodes.

As for -w, my favourite case is https://unix.stackexchange.com/questions/110645/select-lines...

As for -o,

    grep -o ........-....-....-....-............
It may look like Morse code, but what it does is greps UUIDs out.

Ahhh. TIL!

cool stuff, i was messing around with this. To then take that list of exceptions and find them back the actual files again, tack on at the end: `| grep -Fwf - *`

> which shows you the processes and owners of open TCP/UDP ports

naw, that would be `netstat -lntup` (listening, nummeric, tcp, udp, programm)

your mentioned command shows essentially all currently active tcp network streams. https://explainshell.com/explain?cmd=sudo+netstat+-atpn

btw, glances is even more complete than htop


I've been using glances for about a month and am still getting a hang if different UI layouts. It's great for almost any box I'm checking on.

I use both htop and atop, usually htop first as it's more graphical, but atop gives nice IO, wait and NET stats too which is extremely useful.

atop i sweet for overview, but for IO I reach for iotop

nmon is also good. Check it out.

also, dstat

netstat is deprecated and has been for a while, you should be using ss from iproute2. Most of the commands should map directly so it's pretty drop in.

There's are more kinds of UNIX than Linux, and not all of them have deprecated perfectly functional tools.

Only on certain Linux systems is it deprecated. On the BSDs netstat is still the preferred tool.

I like ss if only for the mnemonic "ss 4chan" which sort of but not quite maps to "ss -4tan" ( https://explainshell.com/explain?cmd=ss+-4tan )

Thats glorious, gotta remember that one.

Chan is a japanese name ending for children, various communities have created several Anime mascots over the years. Theyre generally suffixed with that -tan, as a cute misspronounciation of chan.


Btw, 4tan should be that 4chan mascot. Ive seen it previously on sankaku complex, but its been too many years ago. Cant find it right now.

/Edit: i probably should mention that you shouldnt visit sankaku complex at work. Its very... Questionable with nudity

> that 4chan mascot

https://en.wikipedia.org/wiki/Yotsuba%26! (SFW)

This thread has been worth is just to learn about explainshell. I'm so happy that exists.

Uh ok, but ss -atpn isnt very readable on my terminal due to linewrap. Anyone with suggestions ?

    ss -atpn | column -t
Or pipe into `cat`

What is `ss`-equivalent of `netstat -atpn`?

I just use ss -nape most of the time

Prefer netstat -tulpen.

TCP, UDP, listening ports, user, PID and process name, extended detail.

netstat -penult (as in penultimate)

What's the ultimate netstat?

sudo netstat -tuple


I run netstat -tunapl easy to remember

nobody mentioned htop

htop is my trusted standby. Fell in love with netdata though. https://github.com/firehol/netdata - since we all do our best to stay away from getting shells on the servers, netdata is awesome

netdata is very interesting, thank you for sharing it.

It seems to do something very similar to Cockpit, but netdata has way more stuff out of the box.

If you're ssh-ing random boxes they may not have htop.

...my cracking days are long behind me, I no longer ssh into random boxes :)

To be fair, nobody mentions it until someone mentions it.

Can anybody explain to me why this command can return instantly but "lsof -i" sometimes takes ages to complete?

you need -n, otherwise it's trying to RDNS the IP's. It's a dumb default... chatting on the network without you asking while at the same time censoring the data the kernal was using... similarly "ls" might take forever (which matters if it's a big folder and you are piping it's output or just want |head) because it wants to sort (use -f to fix). The ls is a sensible default, often it's for human consumption, and the sort is way faster than a bunch of DNS lookups that could take an arb long time.

lsof has a good case to join coreutils.

A similar issue as with the "-n" flag for netcat exists for "ls": Frequently "ls" is aliased by default in users home directories:

   $ type ls
   ls is aliased to `ls --color=auto'
On slow file systems (for instance, think of shared machines with large directories, NFS and heavy load) this can take ages to give output. Instead, if you just call /bin/ls, this call only calls http://man7.org/linux/man-pages/man3/readdir.3.html and thus gives output promptly.

I've seen \ls used to get the unaliased system version of ls. Likely useful for those commands where you don't want the aliased version and aren't sure if they live in /bin or /usr/bin.

Nice, didn't know about "\ls"! I wonder what's the difference between "\ls" and "command ls". Yes, it's a bit longer to type but the output is the same, I'm asking about what happens behind the scenes.


Genuine question: how many HN readers log on to boxes with user accounts that belong to humans, where some state may have been mutated?

My experience of the last five years is so heavily weighted to (effectively) immutable infrastructure that checking to see who had been on a box hadn't event crossed my mind.

I do that daily. Most of the services we run consist of 1 - 8 application servers ( often closer to 2 than 8), so things like Docker doesn't make much sense. Even though we of cause try to automate as much as possible, using things like Ansible, we often log in to servers directly to verify changes. Database servers are normally manually managed, to some extend, so we'll always login directly.

When I'm on-call and get an alarm on a server, checking that colleagues aren't logged in is normally the first thing you do. If a service fails it's more often than not someone doing maintenance, and they just forgot to tell you, or disable monitoring. And as someone else pointed out, also check disk usage.

Hacker News can be a little blind to the fact that most software projects are rather small and modern servers are really powerful. It's actually pretty rare that someone manages enough infrastructure for a single service that logging isn't a viable option.

Even the word "small" is quite relative. One of my clients is big enough that you've probably heard of them, and their website/app (which is the company's only thing) is one LAMP server. That was only last year upgraded from a Windows 2003 WAMP server on a desktop. I tell friends what I did there and they say "wow you must be really good at Puppet at scale" based on assumptions.

Most people have yet to discover what a tiny little machine can do if you spend some time addressing bottlenecks. I have fond memories of running websites on the cheapest VPSs I could find, and getting very respectable performance from them with little more than cutting down on resource-hungry services, going static html whenever possible and being vigilant about any resources loaded by the browser.

See also https://lowendbox.com/ and https://hackernoon.com/10-things-i-learned-making-the-fastes...

I run a couple of very small scale (mostly static content) web sites and E-mail serving and a few other services on a single "Cheapest VPS" and have never gotten interested in Puppet or Ansible or any of the other things mentioned in this thread. It just seems like adding abstraction and automation on top of things that are not worth abstracting or automating. To me, these things are Yet Another Software That Could Fail. When I need to change a configuration file, I ssh in, sudo vi /etc/blahblah.conf and get on with my life.

I just use versioned Makefiles for my very simple personal projects with my artifacts and configs in git. Pull the repo to the box, and run the make file. I commit config file changes then pull and make as needed. Everything is simple, it's manual automation so there is nothing running, but it's repeatable.

I put the bootstrap into an OS package and my server images point to my personal repo so I can configure run and build time dependencies as needed. At the end of the day, I can get a new server, run update, install my package and walk away and everything should be running, but it takes almost no additional overhead over doing it all by hand the first time.

I also was never interested in Puppet, however I was only interested in Ansible, and only use it as sort of an automated check list when setting up my server, in case I need to rebuild the server, the tedious steps can be automated. But I've never used it for multiple server management.

So what happens when the hard drive fails and you lose all the data and configuration on the box?

Avoiding the huge, fast-changing software for configuration management doesn't mean you can't have CM or high availability on cheap boxes. The OpenVMS approach (see Section VI) combined good filesystem, clustering, optional OS-level virtualization, and distributed lock manager to have clustered systems that ran for years without downtime. Record was 17.


Those few building blocks done in a highly-robust way on one of the stable, Linux platforms could probably achieve the same thing. Just RAID 0, a good filesystem, clustering itself, and backups would get far. I know there's Linux-oriented products out there but I don't know if their availability or failover time have caught up yet.

My VPS host fixes it and I restore from backup.

That’s what RAID and daily backups are for.

Yep. I got to say to my boss recently "you know those 2-4 servers I requested? You can forgot about that now, I optimized some things and we have plenty of capacity now on the one machine we've been using." That's an easy conversation to have.

I share your viewpoint and am currently thinking through a similiar small-scale deployment. How do you handle logging? For single boxes I'd just use logwatch and friends, but for aggregating log output (both system/application logs) from a small-ish Consul cluster I feel the options are complete overkill. I've had a look at ELK, time-series backed stuff (e.g. Prometheus), but all I really want is log aggregation with search capability and optionally Regexp-based alerting.

It seems to me Logstash provides what I want, but I sure as hell won't run 3 JVMs and a Redis instance to aggregate logs.

tl;dr How to handle log aggregation within a small-scale cluster without losing your sanity?

Monitoring and logging are best separated. Prometheus is great even on a small scale. For log aggregation there is the relatively new oklog.

I have been running oklog for a customer successfully. You ought to deploy it like a regular (non-cloud-native) service though: When a server crashes, restore the oklog instance from backups, not spinning a new one.

For small stuff I still like the simple syslog. It’s usually built in and supports aggregating to a single server.

In the past have created a server just with syslog. Adjust all your servers syslog configs to point to that one. Then log in and use grep.

Not fancy. But gets the job done with a single line config change in your syslog configs.

Senior sysadmin here, and I agree this is one of the most common methods. I have also had great success tying in the ossec or pam module notifications into syslog messages that all go to the central syslog (nsyslog/rsyslog etc) server. The problem with the elk and similar stacks imho is lack of security and speed. Things this old school setup doesn't have a problem with. The problem is that too many managers don't like not having gui dashboards... which is why splunk et al have really taken off.

This re-enforces my idea that a purely terminal based business dashboard might be a cool product with a fairly large market. I've been eyeballing some of the go/ncurses work for this.

rsyslog or syslog-ng were preferred these days for better security and performance I thought? Unless you’re using something like stunnel to wrap the syslog messages that is.

If you’re not violently opposed to MongoDB Graylog is very popular. I haven’t heard bad things about it so far besides the MongoDB portion but log aggregation is one of those systems that may be ok with some hiccups from time to time as opposed to an actual primary business data store.

We're kinda big on Splunk, everything that remotely looks like log data get shipped of to Splunk.

I've worked with ELK before and I'm not a fan, the usability is very low compared to Splunk. It's much cheaper though. At a previous employer we switch from Splunk to ELK and the number of searches we did on a daily basis dropped to almost zero. Before that almost every support "ticket" would start with a Splunk search.

You could also try out https://www.humio.com. I only seen it deploy by one customer, but it looks nice.

We use Sumologic and it’s really nice. Much better than ELK. I’ve only used splunk in a evaluation context a long time ago, so I’m not sure how they’d compare. Splunk is just so expensive.

I found Sumologic to lack features that ELK has such as packetbeats. But you still have to manage the Sumologic forwarding agent and keep under your ingest limit. Additionally my mind never exactly flowed with their query syntax. They refreshed the UI recently and I liked it (aside from compounding my overutlization of tabs haha), you now more easily/graphically select time series from the graph. I can see how it is nice to not have to worry about re-indexing and what type of device the underlying data rests on. I have not tried the ELK hosted solution so some of my criticisms could apply to it as well.

We use Humio alongside Splunk and they have an office in SF. Nice people, price is nice too :)

I just have a server dedicated to syslog and have rsyslog running on everything else.

For simple, non-critical stuff this is the simplest solution I've come up with - if you don't need real-time aggregated logs (i.e. you only want to archive them) and you have log rotation configured, you can simply use cron with "aws s3 sync" or rsync for the logs folder.

Check out papertrail.

On my personal dedicated server, I don't have any kind of "modern" things, I do everything the old way, so I do log manually. It's a feature, it's a way for me to learn old-school sysadmin (and I have so little things on here anyway automation is not needed).

For my startup, I often run bash on Heroku because I do migrations manually (again, it's a feature, I'm too inexperienced to have automated migrations that work everytime, I prefer to be already on it if it breaks). Sometime when something breaks I'll also poke around the filesystem (which is a copy, so no fear to break anything).

Basically, I'd say the smaller your team, your uptime requirements and your traffic is, the less you need automation, and the more you are susceptible to login directly to a box (I combine all of that: team of 1, no uptime requirement, not enough traffic to even max the most basic server).

Counterpoint: Even on my private VPS, I have all the configuration as code. It gives me peace of mind knowing that when a server comes crashing down for whatever reason, I can reinstall it and bring all services back online with not more than one hour of time invested. Time is precious.

(Also, when someone asks me "how do you configure X", I can just link them to the corresponding place in my system configuration repo on Github.)

I'd be interested in seeing the config if it's public?

Exactly. The Readme is horribly outdated, but the basic remarks are still true.

I have a small handful of VPSes for personal stuff that, more and more, I'm moving away from manual configuration to using ansible.

The reasons for this are several, but the most pressing are that if one falls over I can spin it up again quickly somewhere else, and I can have a lot of commonality in the configurations between them, so they all have backups configured the same way, or setting up letsencrypt requires editing things in only one place.

It also means I don't have to dig through a bunch of config when I want to work out how stuff is set up three years later, I can just look in one version-controlled directory in a central location.

Not to mention that while configuration management "magic" has taken over (Puppet/Chef - or even something higher level) you still need to set up those and you still need to know where to look when things go wrong.

>My experience of the last five years is so heavily weighted to (effectively) immutable infrastructure that checking to see who had been on a box hadn't event crossed my mind.

In web scale production, you mostly have to worry about your fellow sysadmins troubleshooting the problem, and they mostly won't be too mad about you clearing state.

But not everything is web scale production. Productionizing an app is a lot of work. Yes, yes, "Cloud is reliable!" and that's kinda true if you write your application to deal with any failure at any time. the reality is that the hardware can and will sometimes go away without warning, and you can't call up your oncall and tell them to head to the datacenter to fix it. all that recovery is done at the application layer; you had better hope you managed to make the data redundant enough. The whole idea behind the "cloud" is to take most of the lower level sysadmin work and make developers do it; and that's a fine way to some things, but... not so fine when it comes to other things.

(This is the value proposition of a VPS system rather than a "cloud" instance. when the hardware a VPS is on goes down, some poor bastard's pager goes off, and they are expected to wake up, drag themselves to the datacenter and fix it. The gamble is "is being down for a few hours now and again, when you can reasonably expect to be brought back up in the same configuration cheaper than writing your software such that you can always start over on a new node?" The VPS is for the former, the "Cloud" for the latter.)

Add to that, well, a lot of businesses need to run proprietary software. I personally, well, let us just say that for the last three years, the systems I am dealing with at work involve FlexLM.

so corp and smaller sites are littered with one-off systems... systems where if they break, a pager goes off, and someone fixes the problem. Sometimes that works better than the "web scale" stuff... like I've yet to see a "web scale" posix-ish filesystem that meets the user expectations the way NFS does, and I've never seen a nfs server that didn't require someone on pager.

Our containers are immutable, but the bare metal hosts they run on aren’t.

No, but the "bare metal hosts" should be configured through configuration management and all logs sent "off site". I've been in the same boat and never had to log into a bare metal box. K8s and Ansible will do that for ya.

I work on those "off site" machines that collect your logs and I'm sitting on one as root right now.

Ansible doesn't get you everywhere.

Yikes! We use time series databases, so we simply export the data from them to analytical software or our local machines.

InfluxDB is a simple command to extract what I need and then work with it from there.

Puppet deploys a variety of host-level agents like L7 routing, dynamic config updaters, the scheduler agent (of course), metrics, logging, and tracing collection. Usually they work, but it’s necessary more often than you’d think to find out why one has fallen over and fix it, and to run diagnostic tools to investigate performance anomalies.

The age of immutable inf. did not completely free us from occasional hotfixing production issues, because immutable deployment takes time, and if it's downtime you're accountable (as sysadmin/devops/whatever).

So I am not the only one to have a slow eployment because re-building AMI and re-provisioning everything takes quite some times.

I also had a difficult time to explain that a prod deploy of 30min (image creation, deploy with blue green) is normal for this kind of inf... Did you face the same thing?

Rebuilding AMIs is not a thing you should be doing every deployment. Sounds like you are on AWS so use proper containers on ECS or EBS. Docker itself caches pretty aggressively. Decompose your projects as well so that the independent parts build and deploy without rebuilding everything else in the project that hasn't changed.

At the end of the day, if you're on continuous deployment, a commit should be rebuilding only what it touches. We have 4 min long deployments + 1.5 min tests and I definitely don't think we're optimizing aggressively.

Things get awkward when versioning standards require all application components to have the same version because several version numbers running around is cognitive overhead that engineers can’t afford in many situations. With more than about 10 components I’ve usually seen it turn into “deploy 10 services that have 10 changes, 9 of which have one commit that bump a version number up.”

Many places still keep producing very stateful software (sometimes even very much by choice) that is better off managed through Puppet / Chef rather than an immutable containerized approach. If your software needs to take an hour and a half to shutdown, for example, you have to get a bit creative with your deployment strategies.

A stitch in time, saves `kill -9`

Sounds like you are cutting corners on redundancy. Saves $$$, but risky.

When you have a small number of systems, a small team (possibly one person) and a relatively simple configuration it can be hard to justify spending time and money on a lot of deployment and automation. It isn't that deploying systems as you suggest isn't a better way of doing things. It is just the benefits are far greater at scale. At the scale I typically work it would be over-engineering most of the time.

We have an immutable hosting platform with ansible, but some clients are hosted on their own boxes so we still end up logging into their hosting to sort out their issues (normally they have more problems than we do).

But they aren't interested in investing in more infrastructure when a single LNMP server does the job.

even on immutable hosts it isn't surprising to see somebody has ssh'd in for debugging purposes. they might be attaching a debugger, taking a core dump, or doing a number of other things that could cause a drastic perf hit while not actually mutating the host's state otherwise.

Why take the risk of continuing to run a tainted host, though, if you can just tear it down and spin up a new, clean, untouched one?

I think there’s another level we need beyond treating servers as pets or cattle, which is treating servers as wild animals; after you’ve captured one and interacted with it, you’ve doomed it because now it has the scent of humans on it.

Sure, but that does nothing to prevent the person who invoke the debugger from inadvertently triggering prod alerts, possibly encouraging more folks to ssh in to see what's going on.

Good hiring and training practices prevent people from invoking the debugger on live prod machines

There are times when it has to happen. It certainly shouldn't be an every day occurrence, but even in the best environments, there are times when SHTF only under a production workload, and you need an understanding of why yesterday.

Mostly `root` with ssh-keys for authentication. Some provisioning scripts ( ansible ) that run under root and pretty much that's it.

I haven't seen human users in passwd, since virtualisation kicked in couple of years back.

I do this daily, mainly because most of our infrastructure isn't immutable yet :(

I do. In science we share clusters/supercomputers.

You are at the right hand side of the curve. Professionals do it that way, yes. Many smaller or less-well-managed organizations have a lot more warts.

How, after like 20 years goofing around on linux, have I never heard of `w` ?

Do you know about `comm`? Given two sorted files it will show you in three columns.

    * unique lines to file1
    * unique lines to file2
    * lines common to both files
You can pass it various options to suppress any of the three columns.

I once had an interview at Facebook where one of the problems was easily solved by `comm`. I found it funny that the interviewer, or anyone who reviewed the interview question, had never heard of it. I was a good sport about it though, I ended up writing a janky Perl script that roughly implemented `comm` to solve the problem, which (modulo Perl) was what they wanted me to do.

In that vein, I was asked about implementing n-way merge of logfiles in an interview once. The key insight/recollection they wanted was: use a heap to implement a priority queue. Not sure it was a great question as jumping to employ a data structure like that might suggest premature optimization.

yeah, I'd guess `cat *.log | sort`

This was for Zeus, the high-performance web server guys. So I guess it was a thing for them to optimize in general: a USP.

If you specify that the files are way too big to fit in memory, well, that's a different story.

`comm` at least sounds vaguely familiar. Thanks for reminding me; looks useful.

One time I briefly looked at the man pages of all the binaries under /{bin,sbin} /usr/{bin,sbin} that I didn't know about. A basic Debian install has only 555 binaries (https://pastebin.com/raw/VnrqDdq0). Maybe 100-200 are new to you and are worth checking out. Do it.

This is a good strategy. I grew up on SunOS before Linux. It had (has?) a fantastic set of man pages. You could start with "man intro" and go from there. Looks like it still leads you to the "1M System Administration" section:


The Linux intro man pages are still pretty useless sadly.

I remember I used `w` to check if someone is in the box and then use `talk` to open a chat with that user.

I remember 'w' from reading Cuckoo's Egg some 25+ years ago as a teenager. https://en.wikipedia.org/wiki/The_Cuckoo%27s_Egg

I still do it instinctively on my own boxes.

I thought the same thing. I usually do `who`, `top` and `uptime`. But `w` is far better than `who`.

Same here, although I'm only 14 years in.

You're both newbs. ;) My first Linux box ran kernel 0.99.10.

I run df first, very often something stopped working because the disk space ran out

...and then df gets stuck in uninterruptible sleep (due to a file system hang), and ^C and ^Z does nothing.

Then you know it is most likely a NFS/CIFS issue or hard disk failure.

Downside is you need to log in with a new shell and tread lightly because it's easy for anything to get stuck in that state. Checking the syslog for NFS errors is a good place to start, or inspecting the fstab to see what is supposed to be mounted.

How would you avoid that, and still find out the disk usage?

You wouldn't. If the filesystem is hung, or if some common path is never yielding out of blocking-no-matter-what-calls (e.g. stat()), then the presence of the hang itself would indicate an issue. The isolation process for me would probably be something like:

1. df -h; notice that it hangs.

2. Log in to a new shell, 'strace' the old process or a new one doing the same thing, see what path it was choking on.

3. If the breakage is on an external/network filesystem, reboot the host in almost every case. Unless it was happily completing day 364/365 of some incredibly important task elsewhere, it's just not worth my time to remount a dead share and go clean up everything that was broken trying to talk to the old one. I've had database servers lose some random NFS share that the DB process wasn't using, then crash months later due to PID exhaustion because some monitoring script in cron that kept trying to talk to a somehow-corrupted mountpoint and hanging forever. Yes, timeouts and client programs should be able to handle these failures perfectly in theory. Given my experience, I have very little faith in theory matching up with reality.

4. If it's on an internal drive, check dmesg/syslog (if I can) for any smoking guns. Reboot and see if the problem goes away. If it does, unless I can find something blindingly obvious indicating that the issue was transient and unlikely to reoccur, I'm probably reprovisioning the system after a hardware diagnostic. Even if the server isn't critical and just serves a cat blog or whatever, it's not worth my time and repeated head-scratching to deal with issues like this more than once per host.

5. If I need data off of the questionable filesystem, I'll get it exclusively via a recovery environment; not worth the risk in the case of a flaky/failing drive otherwise (this applies even if the server itself was virtualized). I hope the server had some sort of LOM console set up so I can do that, otherwise someone's getting travel expenses for my trip onsite.

Edits: grammar.

Interesting (well, interesting to me) note on the nfs case, on modern linux, `umount -l` should be able to unmount pretty much anything. You'll often still be left with a pile of processes stuck in uninterruptible sleep depending on the scope of the 'random share', but at the very least it can staunch the bleeding and let you move around.

TBH I get rather claustrophobic when I can't `w` with aplomb.

I had a similar incident (I was able to ctrl-c out of the hanging df -h though). Luckily dmesg gave me something super clear (like `nfs host <blah> unreachable`), so I did a `umount -l` (lazy) on `/mnt/net/<blah>` and things were OK.

Simple ..

   df -h &

# df &


That's one thing I don't need to do. If the disk gets to 80%, I get an email from the monitoring system. 90% and I get a text.

Anecdocte: our sysadmin set similar thing up (at 90%) at one of my boxes. but conflicting configuration of debian os also reserved 15% of capacity for OS, so system became completely unresponsive at 85% full disk, without emailing message about free space - 85% was for our purpose effectively 100% full disk.

Still dont know what lesson I should learn from this story.

Reserved capacity as in `sudo tune2fs <volume> | grep Reserved block count`? Those should already be excluded from available diskspace, so that is kind of interesting.

I am not sure how he was getting free space for email warning, but in final state, running df showed plenty of space on disk, although writing to files signals "no disk space" error.

Reserved capacity is reserved for use by root, so when a process running as root runs df (or any similar command or syscall), then it sees that capacity as available. Kinda useless these days, but was very useful back when you might have server daemons and a bunch of normal users with shell accounts on the same machine.

Huh? I have never seen that behavior, and I can’t reproduce it as described. Did it ever work that way? Do you have any reference for this?

Well, there's man tune2fs:

-m reserved-blocks-percentage Set the percentage of the filesystem which may only be allocated by privileged processes. Reserving some number of filesystem blocks for use by privi‐ leged processes is done to avoid filesystem fragmentation, and to allow system daemons, such as syslogd(8), to continue to function correctly after non- privileged processes are prevented from writing to the filesystem. Normally, the default percentage of reserved blocks is 5%.

-g group Set the group which can use the reserved filesystem blocks. The group parameter can be a numerical gid or a group name. If a group name is given, it is converted to a numerical gid before it is stored in the superblock.

I meant this bit:

> when a process running as root runs df (or any similar command or syscall), then it sees that capacity as available.

I have never seen that. I have only ever seen the “real” available space being shown by tune2fs, not df or anything similar, which have always shown the space available after subtracting the reserved space.

Could you please share how did you setup to be able to get such notification?

Not OP, but we use Nagios XI for such alerting, it provides SMS and email monitoring for infrastructure (disk space as an example) and service monitoring. [1]

Their open source NCPA (Nagios Cross Platform agent) plugin for Windows and Linux hosts is pretty great, though we were stung when we found out it didn't natively support SPARC as of yet unless you compiled your own client from the source (I did). [2]

Plenty of other monitoring services equivalent to Nagios offer equivalent services. Nagios was just the flavour I suggested to my current employer because of my familiarity with the product over my last few employments.

If you don't want to fork out the licensing for the supported version (XI), their open source version is free and relatively easy to deploy using Ansible if you don't mind writing in PHP. [3]

Edit: words, grammar.

[1] https://www.nagios.com/products/nagios-xi/

[2] https://github.com/NagiosEnterprises/ncpa

[3] https://hobo.house/2016/06/24/automate-nagios-deployment-wit...

I will give a simplified example of the only product I've used for this: Zabbix. Disclaimer: I'm not a sysadmin but a developer, who happened to work somewhere they used Zabbix for monitoring all kinds of network devices, databases, services, etc. Perhaps there are better solutions available, I welcome any discussion on that.

Deploying Zabbix roughly consists of setting up one (or more) Zabbix Master servers, and installing a 'zabbix-agent' process on each device you want to monitor. The agent process extracts a variety of statistics about the system and makes them available to the Monitoring server, either in push ("active") or pull ("passive") fashion.

The Master logs all of these statistics over time. You can then define 'Triggers' that apply logical tests to statistics, such as "in the last 5 minutes, was the free diskspace < 10GB". When this happens, it triggers an event.

Then elsewhere you have defined your Notification rules that act upon generated events, to send out an email or text message. https://www.zabbix.com/features#notification

This was obviously really simplified, and there is so much more you can do, but I hope this at least gave you a basic picture.

Have a look at netdata: https://github.com/firehol/netdata

It's very straight forward to setup. I have used Prometheus for the same and so far the experience has been much better compared to Zabbix.

# node_exporter on the client to get metrics # prometheus on server to pull the metrics from node_exporter # alertmanager for raising alerts # grafana on top of it for pretty graphs(optional)

Have a look at nagios. It's a popular open source server/application monitoring tool. You can define custom alerts and monitor basicly everything.

Outside of nagios, you can also use pricier but arguably more fully featured setups like New Relic + PagerDuty.

I don’t I rather run top to see some stats of the system. Mostly I am checking for slow downs and that shows me load mem consumption etc. Diskspace is rarely the case

Most of the time some database connection is laggy

Or, where available, htop.

atop is best top. One of the few bits of software I evangelise.

Writes to replayable binary logfile with 10 minute system-state snapshots and uses process accounting to ensure it see's every process during that time.

Gives more metrics than any other top; including network, disk and all the counters that you have to check the man page to know what they refer to.

Its counterpart atopsar lets you replay the data for specific stats in an easily viewable format; i.e; - atopsar -m - this shows the memory stats for todays logfile in 10 minute increments.

It goes on every single server I manage without exception. With atop you can actually see why it died instead of guessing from old log entries.

Screenshot of atop : https://www.atoptool.nl/images/screenshots/genericw.png

Example output of atopsar:

  # atopsar -m
  *snipped*  2.6.32-896.16.1.lve1.4.51.el6.x86_64  #1 SMP Wed Jan 17 13:19:23 EST 2018  x86_64  2018/03/27
  -------------------------- analysis date: 2018/03/27 --------------------------
  00:00:02  memtotal memfree buffers cached dirty slabmem  swptotal swpfree _mem_
  00:10:02    14027M    928M    839M  6335M    1M   4645M        0M      0M
  00:20:02    14027M    963M    842M  6393M    1M   4641M        0M      0M
  00:30:02    14027M    756M    873M  6617M    1M   4638M        0M      0M
  00:40:02    14027M    576M    871M  6596M    3M   4634M        0M      0M

I sometimes hear about “atop”, wonder “Why don’t I have this installed?”, install it, discover that it starts (and requires) two additional daemon processes, at which point I remember, and promptly uninstall it again.

Yes; the bit that manages the process accounting and the other bit for writing the log files...

Personally I consider two processes and 40MB of ram to be negligible for the benefits it brings.

You can indeed use it as a standalone top without either of these processes too. You're just giving up one of the main benefits (replayable logs) outside of the extra stats.

In short; you're moaning about what exactly?

If you have a tiny fleet of instances, datadog free plan would solve that for you (not affiliated, it's a good product).

> up 23 days > Right there, I can see that okay, the box hasn't been rebooted recently

Is the implication of "recently" that it should have been rebooted every couple of weeks or something?

My desktop is at 54 days (since I moved desk, I think) and picking a random Hadoop node:

> 10:26:47 up 303 days, 11:56, 1 user, load average: 44.12, 50.56, 47.48

It's private, so kernel updates aren't a security issue.

(Keeeping this on-topic, "history" tells me the most frequent thing I do on this node is "sudo iftop"; we've been doubting the accuracy of our monitoring system's network utilization graphs.)

I think her thinking was "the problem started recently (~days), did the box get rebooted recently (~days) which might indicate when the problem started", rather than it should have been rebooted recently.

w; df; dmesg; top

usually there's a loud sob somewhere in between.

reading w df in my head made me laugh

> If you want to impress me, set up a system at your company that will reimage a box within 48 hours of someone logging in as root and/or doing something privileged with sudo (or its local equivalent). If you can do that and make it stick, it will keep randos from leaving experiments on boxes which persist for months (or years...) and make things unnecessarily interesting for others down the road.

Ferrari does this. They do a lot of experimentation on their most expensive internal test equipment, and every now and then the whole box is re-imaged automatically, even if it's completely locked down from outside. It's their internal staff who is corrupting/improving the system. Only if it's a really good and well-tested improvement they will make it stick.

Anybody running Chaos Monkey (from Netflix) does this, at lesat for their stateless services.

I do that too. I probably wouldn't if I hadn't learned on a shell server where that was how you found out who else was up.

i did not know w was a command. I've used the 'last' command https://www.cyberciti.biz/faq/linux-unix-last-command-exampl...

I never even knew about that command...

Me neither. I just asked two colleagues (one on MacOS, one on Ubuntu) and got the same “huh, I never knew?” response I had.

Sure there are tons of unknown commands on any OS, but a one-letter command you've never heard of somehow amplifies the amazement.

In a (normal/typical) shell, hit "<Tab><Tab>y" and be amazed.

My standard set of commands in context of troubleshooting, in no particular order is * w * last * dmesg

Related, "Linux Performance Analysis in 60,000 Milliseconds":


I stick to serverless setups and platforms like Heroku wherever I can. The whole idea of state being stored on a web server or having to SSH in to them to do any form of admin makes my skin crawl now.

It's not because 'there is no state' - you just outsourced state(s) to the third party.

I think it's more the case that typical e.g. VPS setups introduce state where you shouldn't have state at all.

Web servers for example should typically have minimal state for scalability and robustness but for most VPS setups this is not the case. If the VPS got wiped it could take days of work to get up and running again, and if you wanted to scale horizontally you'll have some reengineering to do. You could try and replicate something like Heroku yourself to minimise state on your web servers but it'll take you a lot of time and won't be as robust.

I use the same approach when troubleshooting/getting into hairy code - git blame ("annotate" in IntelliJ) first, gives a lot of useful context!

On FreeBSD systems there are two great commands that are not available on other systems.

These are 'gstat' and 'top -m io' commands, both I/O related.

Often in top/htop there is not much happening but the server is very slow, a lot of the times its because of I/O operations.

The 'gstat' command will tell You (besides other useful statistics) how much the storage devices are loaded:

  # gstat
  dT: 1.001s  w: 1.000s
   L(q)  ops/s    r/s   kBps   ms/r    w/s   kBps   ms/w   %busy Name
      1   9679   9614   4807    0.1     63    671    0.2   82.3| ada0
      0      0      0      0    0.0      0      0    0.0    0.0| ada0p1
      0     65      0      0    0.0     63    671    0.2    1.4| ada0p2
      0      0      0      0    0.0      0      0    0.0    0.0| ada0p3
      0      0      0      0    0.0      0      0    0.0    0.0| gpt/boot
      0     65      0      0    0.0     63    671    0.2    1.5| gpt/sys
      0      0      0      0    0.0      0      0    0.0    0.0| gpt/local
      0      0      0      0    0.0      0      0    0.0    0.0| zvol/local/SWAP

The 'top -m io' show which processes does how much I/O:

  # top -m io -o total 10
  last pid: 51154;  load averages:  0.31,  0.31,  0.28 up 3+18:01:00  14:58:15
  54 processes:  1 running, 53 sleeping
  CPU:  2.4% user,  0.0% nice, 15.3% system,  5.3% interrupt, 77.1% idle
  Mem: 345M Active, 1236M Inact, 153M Laundry, 2158M Wired, 3903M Free
  ARC: 834M Total, 46M MFU, 295M MRU, 160K Anon, 5006K Header, 488M Other
       67M Compressed, 274M Uncompressed, 4.08:1 Ratio
  Swap: 4096M Total, 4096M Free
  51021 vermaden       6005     16   6005      0      0   6005  99.92% dd
  51154 vermaden          8      9      5      0      0      5   0.08% top
  51036 vermaden          6     10      0      0      0      0   0.00% xterm
  50907 vermaden          0      0      0      0      0      0   0.00% zsh
  50905 vermaden          0      0      0      0      0      0   0.00% xterm
  50815 vermaden          0      0      0      0      0      0   0.00% zsh
  50813 vermaden          0      0      0      0      0      0   0.00% xterm
  50755 vermaden          0      0      0      0      0      0   0.00% tail
  41780 vermaden          0      0      0      0      0      0   0.00% leafpad
  41255 vermaden         29     11      0      0      0      0   0.00% firefox

Another command that is very useful on FreeBSD is 'vmstat -i' which show how much interrupts are happening:

  # vmstat -i
  interrupt                          total       rate
  irq1: atkbd0                       75135          0
  irq9: acpi0                      2575929          8
  irq12: psm0                       135060          0
  irq16: ehci0                     1532065          5
  irq23: ehci1                     3265677         10
  cpu0:timer                     102772345        317
  cpu1:timer                      94199942        291
  irq264: vgapci0                   370466          1
  irq265: em0                         7017          0
  irq266: hdac0                    1904427          6
  irq268: iwn0                   148690342        459
  irq270: sdhci_pci0                   147          0
  irq272: ahci0                   20875039         64
  Total                          376403591       1161

I always suffer when I have to debug Linux systems because of lack of these commands.

Regards, vermaden

You do know about “iotop”, right?

Thanks You for suggestion, now the answer is yes, nice alternative to 'top -m io' on Linux.

dstat, iotop, htop - lots of similar tools, giving you the same data on linux

Thanks You for suggestion, now the answer is yes, nice alternative to 'top -m io' on Linux.

While 'dstat' gives some information its usefulness (at least for me) is far from 'gstat' outout.

"some information"? Did you look at all the plugins and output options? gtop is cool, but I typically don't run node on all my servers. Call me old-fashioned...

My first reaction after logging into unknown *nix machines.


uname -a



df -h

free -m

cat /proc/cpuinfo



ps aux

then check appropriate logs or dmesg etc

You say *nix machines, but some of your commands are Linux specific.

Only two, 'free' and 'cat /proc/cpuinfo'. Everything else can work on both.

I actually have a profile.d entry that runs w on login any time I open a shell on any machine in my infrastructure.

There used to be time when the first thing I did was `sudo reboot` and it actually worked just fine many times.

"w" & "last" are first for me. Then "top" and "uname"

Yep w for me as well. History after.

And next, I usually run "top"... quick snapshop of whats going on.

sudo dmesg -w -H --level=err

I run history first, followed by df then finally I run htop.

atop creates world readable log files. Does anyone else think this is a security vulnerability?

They have nearly the same information a normal user could get by running atop themselves, which reads the world-readable virtual files found in /proc. If you are using something like selinux to restrict access to /proc files, the same system could be used to restrict access to the /var/log files.

This is the sort of article that I keep coming back to HN for. It's not politics. It's pure and simple technical advice with reasonable back and forth opinions from the community (other than the "if you want to impress me" guy). And nobody wants to take my 2A right, sorry, my right to use 2FA!

I do 'ls' as a reflex I don't know why. For network monitoring I like:


nload -u K

There are two things I don't like here:

- the author seems to call out specific individuals, by name, to their team leads, based on where they were ssh'd in, instead of bringing up the issue with that person first and asking for the logic of why they were on the box doing the thing (sounds like a lot of assumptions combined with finger pointing)

- it sounds like there's no well-configured monitoring or observability at the DC/rack/machine level involved, at all, which is surprising in a modern enterprise setup

> the author seems to call out specific individuals, by name, to their team leads, based on where they were ssh'd in, instead of bringing up the issue with that person first and asking for the logic of why they were on the box doing the thing (sounds like a lot of assumptions combined with finger pointing)

I'm not sure why you would assume that. She specifically says "The next thing I'd do is to go get in touch with that person."

Perhaps you're keying off "I've been able to track down some well-meaning but ultimately flawed attempts at fixing things that then blew up and became something much bigger. The folks who I pinged about it were amazed that I somehow had managed to "guess" that a specific member of their team had been poking at a specific box"? But keep in mind, that's specifically events that became a large issue. Is it not appropriate to notify management as to the cause of the issue? Either it's a first time mistake or not something the person may necessarily have known to look out for, in which case management should be lenient, or it's the latest in a string of events and management should possible take some other action.

If nothing else, it allows management for that other team to say "hey, we don't need to be messing with this aspect of the server. Either contact the team whose responsibility it is and get them to do the work, or get them to sign off on it first."

On call person was on a plane. They did something using intermittent connectivity and made a mistake. Other person on the ground is helping until the first one lands. I tell #2 about a box touched by #1 and ask them to have a look.

They did and they figured it out. Outage resolved.

Why did you automatically assume I ratted them out to management? At no point does the story go there.

I’m really curious, since misunderstandings like this can really poison a working environment when people think you’re doing things you’re not. I want to know what sent you down the wrong path here.

Nah, you're fine, OP.

Commenters tend to proclaim bad intentions when none is present when they either skimmed without reading or that they are lashing out to compensate for some weird insecurity, e.g. "I caused an outage once and I didn't want anyone to ask me and find out! How dare you want to know!?"

Thanks. I ask because I’m pretty sure I tripped over this bigtime in recent history.

When all you do is wander around looking for broken stuff to help fix, imagine the above sequence repeating itself.

For whatever reason,

> "I've been able to track down some well-meaning but ultimately flawed attempts at fixing things that then blew up and became something much bigger. The folks who I pinged about it were amazed that I somehow had managed to "guess" that a specific member of their team had been poking at a specific box"?

read like "I didn't like what someone did on a machine I had to troubleshoot, and told their manager" to me.

I was also reading this prior to coffee, mea culpa.

After running w, “The next thing I'd do is to go get in touch with that person. It would be foolish to continue when the answer might be a few short chat messages away.”

> If you want to impress me, set up a system at your company that will reimage a box within 48 hours of someone logging in as root and/or doing something privileged with sudo (or its local equivalent). If you can do that and make it stick, it will keep randos from leaving experiments on boxes ...

It’s called Chef.

Rachel’s starting point here is a fair few steps ahead of ”it’s called chef”. For one, chef only fixes the things that you explicitly tell it to. When you have enough machines and enough people poking at them, you’re more or less guaranteed that someone somewhere will have gotten a machine or three in a state chef can’t recover from — hence her suggestion of reimaging.

Always pxeboot, then "re-imaging" is a matter of "turn it off and on again".

If you have a hardware failure how would you rebuild?

Of course this all takes time to implement and manage -- it's a tradeoff.

How do you manage the network boot server? How will pxeboot interact with hosting your rack switch images?

High availability IP for your dhcp for "next-server", so you can boot one server from another one.

Mikrotik routers and switches can boot from dhcp (or bootp?), but yes a typical switch can't.

Not a network person, but I assume you can give fine grained enough control that you can't do a "copy running-config startup-config" on a cisco switch, so have a startup config that boots to a known basic state then tftps it's config from your HA dhcp server.

> If you want to impress me, set up a system at your company that will reimage a box within 48 hours of someone logging in as root and/or doing something privileged with sudo (or its local equivalent).

Why revert it in the first place? Why not deny the changes? Doesn't this indicate that the wrong people have root access?

sometimes the best way to test a fix to something, before you make it permanent in the deployment-as-code, is to test it on the box.

This just makes you sure actually go back and change the deploy code, else it breaks in ~2 days.

You could just have one or more specific development/test box(ex) to try changes on, and then implement those on production.

Chef doesn’t reimage anything.

If you want to impress me, go serverless.

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