Turn off almost all of dig's output except for what you'd see in a zone file. This can also be put into ~/.digrc.

This command is somewhat similar to 'nice', but constrains I/O usage rather than CPU usage. In particular, the '-c3' flag tells the OS to only allow the process to do I/O when nothing else is pending. This dramatically increases the responsiveness of the rest of the system if the process is doing heavy I/O.

There's also a '-p' flag, to set the priority of an already-running process.

The Linux /dev/full file simulates a "disk full" condition, and can be used to verify how a program handles this situation.

In particular, several programming language implementations do not print error diagnostics (nor exit with error status) when I/O errors like this occur, unless the programmer has taken additional steps. That is, simple code in these languages does not fail safely. In addition to Perl, C, C++, Tcl, and Lua (for some functions) also appear not to fail safely.

This command install Apache 2 and other utilities on CentOS

The backslash avoids any 'rm' alias that might be present and runs the 'rm' command in $PATH instead.

In a misguided attempt to be more "friendly", some Linux distributions (or sites/etc.) alias 'rm' to 'rm -i'. Unfortunately, this trains users to expect that files won't actually be deleted until they okay it. This expectation will fail with catastrophic results when they use other distributions, move to other sites, etc., and doesn't really even work 100% even with the alias. It's too late to fix 'rm', but '\rm' should work everywhere (under bash).

creates a new tab for each of N servers in listofservers.txt and ssh's to said servers

then, try the "send to all sessions" feature of konsole to do the same work on all servers at the same time. BIG time saver, but be careful!

The last ; is important. example:

time { rm -rf /folder/bar && mkdir -p /folder/bar ; echo "done" ; }

command is a bash builtin

converts encoding of a file to unix utf-8

useful for data files that contain what would be usable ascii text but are encoded as mpeg or some other encoding that prevents you from doing common manipulations like 'sed'

Ever logged into a *nix box and needed to know which webserver is running and where all the current access_log files are? Run this one liner to find out. Works for Apache or Lighttpd as long as CustomLog name is somewhat standard. HINT: works great as input into for loop, like this:

Very useful for triage on unfamiliar servers!

puts command in background and sends its output to nohup.out file

it will not die if you log out fromyour shell session ;-)

Using +F will put less in follow mode. This works similar to 'tail -f'. To stop scrolling, use the interrupt. Then you'll get the normal benefits of less (scroll, etc.).

Pressing SHIFT-F will resume the 'tailling'.

above line in .bash_profile will give you window title in putty or terminal client when you login to your remote server

Ever need to know why Apache is bogging down *right now*? Hate scanning Apache's Extended server-status for the longest running requests? Me, too. That's why I use this one liner to quickly find suspect web scripts that might need review.

Assuming the Extended server-status is reachable at the target URL desired, this one-liner parses the output through elinks (rendering the HTML) and shows a list of active requests sorted by longest running request at the bottom of the list. I include the following fields (as noted in the header line):

Seconds: How long the request is alive

PID: Process ID of the request handler

State: State of the request, limited to what I think are the relevant ones (GCRK_.)

IP: Remote Host IP making the request

Domain: Virtual Host target (HTTP/1.1 Host: header). Important for Virtual Hosting servers

TYPE: HTTP verb

URL: requested URL being served.

Putting this in a script that runs when triggered by high load average can be quite revealing. Can also capture "forgotten" scripts being exploited such as "formmail.pl", etc.

convenience.

Use carefully have rm -rf ;-)

It would be nice if commandlinefu.com had a better domain name. Will they pick one of the above; We'll see.

FreeBSD version of the Linux command

The "mdconfig" command creates a device and prints the name (typically "md0"). Just append that to "/dev/" and mount.

Once unmounted, you can unconfigure the device with

using "0" for md0, "1" for md1, etc.

tail would be considered dull, but pair this with being able to push out unix commands over ARD, and life gets easier. (Same can be said for my TimeMachine scrape command, http://xrl.us/begrzb)