After administering Unix or Unix-like servers, what tools (command-line preferably) do you feel you cannot live without?
GNU screen - essential when you're managing large numbers of systems and don't want to have a dozen terminal windows open.
Some I know that I cannot live without...
tee - allows simultaneous writing to STDOUT (standard output) and a file. Great for viewing information and logging it for later.
top - the task manager of UNIX, gives a great overview of the system.
tail -f - allows you to view appended data as a file grows, great for monitoring log files on a server.
grep - Global Regular Expression Print, great for searching the system for data in files.
df - reports disk usage of current filesystems.
du - reports disk usage of a certain file/directory.
less - needed to view man pages! also useful for viewing output of commands in an easily seekable manner.
vim/Emacs/nano/pico/ed - whatever your text editor of choice may be, self explanatory of why it's needed.
For those who don't know, 'less' is an updated version of 'more'. more was limiting because you could only move forwards over a file whereas less can scroll backwards too. Ah the humour... :-) May 4, 2009 at 11:18
8Another useful but little known feature of less is that you can always use the 'v' command to start editing the file you're currently looking at. Mnemonic is 'v' for 'vi'.– dr-janJun 1, 2009 at 14:20
And if you don't like
less, you can always try
most.– drybjedJun 1, 2009 at 14:41
My preferred PAGER now is actually w3m. It has all the features of less, and can double as a text mode web browser :-) I have also used a bash function to use vim in read only mode (this way I get nicely colored diffs for instance). The bash function is used just to decide whether to provide '-' (for read the stdin) or not (in case we are paging a file). Works like a charm, except for man pages where nroff does overstrike...– njsfJun 4, 2009 at 20:21
htopis a "better" version of
top. Nov 10, 2011 at 5:49
lsof to determine which processes are using a file or directory (useful when trying to figure out what is preventing a device from being umount'd)
netstat to determine which processes are using network connections (especially useful when trying to figure out which daemon is bound to a certain port)
1If you have lsof, you don't need netstat. Just use lsof -i– vartecMay 5, 2009 at 10:35
lsof -n is my favorite invocation. I pipe it to grep to pare it down Jul 15, 2009 at 20:41
Learn all the basic tools, but learn Perl.
Perl is ideal for manipulating text, and since un*x operators live on text files, pipes, input and output, Perl is a great fit.
The added bonus is Perl is cross platform and if you have to do some work on a windows box you have an easily installable (just drop a Perl directory on the server) language that you already know.
And on that train of thought, get Cygwin as well. If you are a un*x admin and have to work on a windows box (even your desktop) having ls, rm, grep, sed, tail etc save you a lot of time when switching OS's.
The forgotten grandfathers of modern systems scripting. I know Perl gets most of the love (along with Bash scripting, Python, Ruby, and [insert your favorite scripting language here]), and don't get me wrong, I love Perl. I make use of it almost daily.
But sed and awk should not be forgotten, overlooked, or ignored. For a lot of cases, sed and awk are the best tools for the job. Quick examples are command line filtering with sed, and quick and dirty log processing with awk. Both could be done in Perl, but will require more work and development time.
rsync, especially in concert with ssh. It allows simple efficient copying of files from host to host. How did we ever cope without ssh and rsync? :-)
- Test if TCP services are listening.
- Perform transactions against plaintext protocols such as SMTP.
- Quick insecure data transfers between machines.
- Telnet client emulation.
The network swiss army knife, as they say.
I've recently started using socat as netcat's replacement and I've been amazed at the number of options it gives you. Definitely worth checking out, despite scary amount of switches and weird syntax.– MarcinNov 23, 2010 at 14:54
Face it - sooner or later you'll deal with the network as well. mtr, tcpdump and tshark are really useful for seeing what's happening.
For quick scripts, automation, etc:
To connect to your *NIX server:
- Open SSH (Linux client)
- Putty (Windows client)
+1 for... well all of it really but Perl especially. *nix, Windows or Mac, I can't imagine what I would do without it. Apr 12, 2010 at 9:32
I use most of the tools already listed, but here's one no one has touched on yet:
Puppet - system for automating system administration tasks
Most of the standard ones are included in other answers, so I'll go fo non-standard ones:
A couple of handy tools I haven't seen mentioned yet:
- dstat --nocolor (overview of cpu-, disk-, net-usage)
- iftop (nice dynamic overview of network traffic)
- ccze (colour logfiles nicely)
- ssh tunnels (can be useful once in a while; see the manual; -R)
- expect (automate interactive, chatty dialogy interfaces, nice if you're in a pinch)
+1 "tail -f <file> | ccze" = amazing way of reading log files.– LinOct 8, 2009 at 6:26
+1 for dstat. Best replacement for vmstat, iostat, etc. out there. Jan 25, 2012 at 23:02
ClusterSSH controls a number of xterm windows via a single graphical console window to allow commands to be interactively run on multiple servers over an ssh connection.
... and since ClusterSSH is written in Perl, perhaps you should learn Perl. May 6, 2009 at 14:37
What's the difference between ClusterSSH and GNU screen? or are they different implementations of the same concept? Nov 10, 2011 at 5:51
Gives you a great overview of system behaviour.
pv: Displays the progress of long operations that can be redirected. http://www.ivarch.com/programs/pv.shtml
Useful then you want to monitor something that is going to take ages, like copying/compressing a raw block device over the network (which is how I take paranoia backups of my 8Gb netbook before tinkering with anything major like tweaking with file system settings).
Also: I'll second votes for ssh, rsync, screen, htop and netcat as mentioned by people above - all of which are more important than pv but pv had not been mentioned yet. In fact pv is often a useful addition when piping stuff to or from to netcat.
pvcan be a handy tool, but beware of overusing it. Passing the data through it absolutely has a performance impact (all the data has to pass through another program). At my last job, we did a lot of log processing. One of the guys decided to start putting pv in all the log processing scripts, until we discovered that it added about 15% to the processing time for them. Now it's only used for jobs that take less than a few minutes, or that have an existing resource limitation (such as crossing a slow network connection). Jan 25, 2012 at 23:09
Good point Christopher, though I've never seen it cause as much as a 15% performance change (then again, most of what I use
pvfor is disk or network I/O bound rather than CPU/memory bound). The same arguement is the key one against excess use of
cattoo (I sometimes use cat when not actually needed just to make things read nicely left-to-right, but the extra in-memory data copying via the pipe and context switching can have a measurable performance impact). Jan 26, 2012 at 11:52
Yeah, I do the same thing. Most of my excessive
catuse comes from starting with
cat foo, followed by hitting the "up" arrow and then adding
| [command]to my previous line. I know I'm taking a (small) performance hit by keeping the cat in there, but leaving it requires less effort than rewriting/retyping the command to be
[command] < foo. Not a concern for (most) ad hoc command line work, but not ideal for scripts (same as how I feel towards
pv, I guess). Jan 30, 2012 at 18:39
ssh, Vim, htop, su, Python, ls, cd, screen, du, tar :)
tail -f is useful.
Some that haven't been mentioned before:
piping the output of tar to another utility, to tar running on the same box, or to tar running over SSH is my favorite old-school Unix move for moving files from one place to another.
This also gives you the Windows-style option of copying one folder to another and ending up with all of the files in the source and destination directory.
zsh as a shell
It is especially efficient with grml.org's extensions/setup.
iotop, is a top-like program to monitor I/O accesses to your disks.
Most of these tools are made much more powerful using Bash "programmable completion" - so you can tab-complete things like commandline options, or say the name of a package with "apt-get install". It will also limit what you tab-complete for relevant files - for example, "unzip" will only complete supported archive files.
It really is the mutts - if you have never tried it you probably just need to fiddle your .bashrc:
if [ -f /etc/bash_completion ]; then . /etc/bash_completion fi
Certainly this is true on Ubuntu and Debian. You may need to get the package on some Linux distributions.
Some additional answers can be found in this similar question
A few things overlooked I wanted to mention.
- vim -d split screen console diff that makes it very easy to see the differences in a file
- pdsh allows you to easily run a command over as many systems as you want either serial or parallel(I am a cluster admin. I can't function without it.)
- nmon is like top on crack. It gives you a great idea of what is going on on a system on a single screen. You can see disk I/O, network I/O CPU usage, and memory usage real time. At the very least a real fun thing to play with when profiling a system.
Oh, and I forgot to mention, when scripting, I believe you should always use Korn. I hate Korn(Not the band. I love the band:-P) but it's literally everywhere. You can take a script and move it between Solaris, AIX and Linux and not have to worry about whether or not the admin had the decency to install Bash.
One tool sometimes very handy is nohup. I use it to run scripts that last for a long time using remote SSH clients.
man - to read the man pages.
elinks - to check google, cause I sure as hell cant remember everything.
And attention to detail & tenacity, because without them I just waste time.
screen is a must, especially with a good .screenrc file. I have it configured to display visually which window I'm in and can move between them with Ctrl+Arrow. For a single ssh session and multiple shells, it is a life saver.
I love AWK as well as "for" on the command line.
Especially to build up a list of commands I want to run and then execute them all at once.