This isn’t intended to be comprehensive at all. I’ll just be listing commands that I sometimes but not often use to do miscellaneous administrative tasks.
Passwordless SSH
Between trusted hosts, I want to allow passwodless access via ssh. To do this, generate RSA key pair:
$ ssh-keygen
When prompted, accept the defaults unless things need to be changed. Copy the public key just generated in ~/.ssh/id_rsa.pub on the local host. Login to a remote host, and append the key to ~/.ssh/authorized_keys. Next time I login to that host, I will not be prompted for password.
Linux Equivalent of open on Mac OS X
One command I like on Mac OS X is open, which open a file with an associated default application. There is a command called xdg-open which does the same thing. Make an alias to it so it acts like the one on Mac:
alias open='xdg-open'
Put this in ~/.bash_aliases.
Find the UUID of Devices
$ sudo blkid
Securely Erase Hard Drive
# fdisk -l # check hard drives file systems # shred -vfz -n 20 /dev/sdb # secure erase /dev/sdb
Redirect Output to Multiple Processes
Use “tee >(…)”:
$ ls -A | tee >(grep ^[.] > hidden-files) >(grep -v ^[.] > normal-files)
This example comes from this article.
Repeating Same Operation on Many Files
$ for i in *.txt ; do echo $i ; done
Recursively Do Something on Files/Directories
Find all files under a root path:
$ find /path/to/root -print
Change all directory permissions to 755:
$ find /path/to/root -type d -print -exec chmod 755 {} \;
Change all file permissions to 644:
$ find /path/to/root -type f -print -exec chmod 644 {} \;
Change all files and directories with 777 permissions to 755 permissions:
$ find /path/to/root -perm 777 -print -exec chmod 755 {} \;
Show the n-th (e.g., 9th) Line of a Text File
$ sed -n '9p' somefile
Send an Email Message
Provided the mail service is set up properly, a simple message can be sent quickly on command line.
$ echo "message body" | mail -s "subject line" your@mail.com
This is useful when I want to get an email notification when a very time-consuming job finishes. For a time consuming job, sometimes it’s desirable to email the output from the job. I can redirect both standard output and standard error to the email message body by:
$ someprogram 2>&1 | mail -s "job is done" your@mail.com
Keep a Process Running without Hangups
When starting a process on a remote host (e.g., over ssh), that process is killed when you logout of the session. To keep it running there, use nohup:
$ nohup somecommand &
Kill All Processes with a Given Name
$ kill -9 `pgrep someprogramname`
This will kill all the processes with the name someprogramname; see the man page for pgrep for more info.
Change Run-Level Configuration for Init Scripts
$ sudo sysv-rc-conf
This will provide an easy-to-user user interface to configure init scripts. Useful when I want to stop KDM from running at boot, for example.
Find Out How Long the System Has Been Running
$ uptime
Search for Filename in Debian Packages
The Debian packaging system is obviously useful, but I often struggle to find to which package a particular command belongs. I can search for by filename:
$ sudo apt-file search somefilename
To do this, the command apt-file needs to be installed if not already:
$ sudo aptitude install apt-file $ sudo apt-file update
Clear Apt Package Cache
The /var partition may quickly fill up with downloaded .deb packages and if the partition size is small, occasional cleanup will be necessary. If I wish to just remove .deb files that are no longer relevant, do
$ sudo aptitude autoclean
If I need to remove all .deb files, then
$ sudo aptitude clean
The latter is okay as long as I don’t mind downloading many of them again when I need to update the system via the update-upgrade sequence, for example.
View the CPU Information
$ cat /proc/cpuinfo
Bash Scripting
Get the Absolute Path to the Script’s Current Directory
DIR="`dirname $BASH_SOURCE`" ABSDIR="`cd $DIR; pwd`"
Get the Host Name
HOST="`hostname -f`"
More to come.
