Command Line Kung Fu (2014)

System Administration

Display Mounted File Systems in a Tabular Format

$ mount | column -t

The output of the mount command is not formatted in an easy-to-read manner. To make each column line up, pipe the output of the mount command to "column -t". By default mount displays all mounted filesystems, even the pseudo-filesystems like /proc and /sys. To limit output to a filesystem type, use the -t option and provide a type.

$ mount -t ext4

/dev/mapper/sysvg-lv_root on / type ext4 (rw)

/dev/sda1 on /boot type ext4 (rw)

$ mount -t ext4 | column -t

/dev/mapper/sysvg-lv_root on / type ext4 (rw)

/dev/sda1 on /boot type ext4 (rw)

Kill All Processes for a given User or Program

$ pkill -9 command

$ pkill -9 -u user command

If you need to kill several processes with the same command, use the pkill command. If you only want to kill processes for a given user, use the -u option. Pkill will only kill the processes when all the criteria match. That means you can kill all of a given process that is being run by a specific user.

$ ps -ef| grep http | grep -v grep

root 12253 1 0 10:55 ? 00:00:00 /usr/sbin/httpd

apache 12255 12253 0 10:55 ? 00:00:00 /usr/sbin/httpd

apache 12256 12253 0 10:55 ? 00:00:00 /usr/sbin/httpd

apache 12257 12253 0 10:55 ? 00:00:00 /usr/sbin/httpd

apache 12258 12253 0 10:55 ? 00:00:00 /usr/sbin/httpd

apache 12259 12253 0 10:55 ? 00:00:00 /usr/sbin/httpd

apache 12260 12253 0 10:55 ? 00:00:00 /usr/sbin/httpd

apache 12261 12253 0 10:55 ? 00:00:00 /usr/sbin/httpd

apache 12262 12253 0 10:55 ? 00:00:00 /usr/sbin/httpd

$ sudo pkill -9 httpd

$ ps -ef| grep http | grep -v grep

$ ps -ef| grep ssh | grep -v grep

root 1202 1 0 Apr06 ? 00:00:00 /usr/sbin/sshd

root 12339 1202 0 11:22 ? 00:00:00 sshd: jason [priv]

jason 12342 12339 0 11:22 ? 00:00:00 sshd: jason@pts/0

root 12368 1202 1 11:23 ? 00:00:00 sshd: bob [priv]

bob 12372 12368 0 11:23 ? 00:00:00 sshd: bob@pts/1

$ sudo killall -u bob sshd

$ ps -ef| grep ssh | grep -v grep

root 1202 1 0 Apr06 ? 00:00:00 /usr/sbin/sshd

root 12339 1202 0 11:22 ? 00:00:00 sshd: jason [priv]

jason 12342 12339 0 11:22 ? 00:00:00 sshd: jason@pts/0

Repeat a Command until It Succeeds

$ while true

> do

> command && break

> done

The while loop will continue until the condition is false or it encounters a break. In his case we effectively create an infinite loop and break once our chosen command succeeds. If you want to keep pinging a host until it responds, you could use this while loop.

$ while true
> do
> ping -c 1 -W 1 remote-host >/dev/null 2>&1 && break

> done ; echo "Remote-host is up at $(date)."

Remote-host is up at Fri Apr 11 21:30:29 EDT 2014.

If you're waiting for a file to show up on your server, you could use this while loop.

$ while true

> do

> ls /svr/ftp/incoming/payroll.txt.gpg 2>/dev/null && break

> done; echo "Payroll file arrived at $(date)."

Payroll file arrived at Fri Apr 11 21:33:23 EDT 2014.

Find Who Is Using the Most Disk Space

$ sudo du -s /home | sort -n

This command will display the person who is using the most disk space in their home directory. The users will little disk space will be displayed at the top of your screen and the users using the most disk space will be displayed at the bottom.

$ sudo du -s /home/* | sort -n

32 /home/pat

32 /home/terry

40 /home/jim

40 /home/jimbob

44 /home/oracle

19184 /home/adminuser

22208 /home/bob

65132 /home/jason

If you are looking for a more graphical way to display disk usage, check out the neat utility ncdu.

$ ncdu /home

ncdu 1.10 ~ Use the arrow keys to navigate, press ? for help

--- /home -------------------------------

37.9GiB [##########] /ryan

1.3MiB [ ] /lucas

Total disk usage: 37.9GiB Apparent size: 37.8GiB Items: 156055

Find the Files That Are Using the Most Disk Space

$ find / -type f -exec wc -c {} \; | sort -n

Use find to execute the "wc -c" command against each file, revealing it's size in bytes, and then sort that output. The smallest files will be displayed first, and the largest files will be displayed last. If you are scanning every file on a system, this command could take awhile to complete.

$ sudo find /var -xdev -type f -exec wc -c {} \; | sort -n

0 /var/cache/apt/archives/lock

...

2572437 /var/lib/dpkg/available-old

2573098 /var/lib/dpkg/available

38433001 /var/cache/apt/pkgcache.bin

39872802 49659904 /var/cache/apt-xapian-index/index.1/termlist.DB

62783488 /var/cache/apt-xapian-index/index.1/postlist.DB

List Processes, Sorted by Memory Usage

$ ps aux | sort -nk 4

Use this command to find the processes that are consuming the most memory. The processes using the least amount of memory will scroll off the top of your screen and the ones consuming the most amount of memory will be just above your shell prompt.

In this example, mysqld is consuming 1.3% of the memory on this host.

$ ps aux| head -1

USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND

$ ps aux | sort -nk 4 | tail -5

root 2969 0.0 0.3 11856 3228 ? Ss 17:16 0:00 sshd: jason [priv]

root 4576 0.0 0.3 11364 3380 ? Ss 17:52 0:00 /usr/sbin/httpd

root 958 0.0 0.3 20844 4084 ? Ssl 00:00 0:00 NetworkManager

68 1003 0.0 0.4 17104 4268 ? Ssl 00:00 0:00 hald

mysql 4546 0.0 1.3 136332 13848 pts/0 Sl 17:52 0:01 /usr/libexec/mysqld

List Processes, Sorted by CPU Usage

$ ps aux | sort -nk 3

Use this command to find the processes that are consuming the most CPU. The processes using the least amount of CPU will scroll off the top of your screen and the ones consuming the most amount of CPU will be just above your shell prompt.

In this example, mysqld is consuming 94% of the CPU on this host.

$ ps aux| head -1

USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND

$ ps aux | sort -nk 4 | tail -5

root 2469 0.0 0.3 11856 3228 ? Ss 17:16 0:00 /usr/sbin/fcoemon

root 452 0.0 0.3 20844 4084 ? Ssl 00:00 0:00 master

root 5571 2.1 0.3 11364 3380 ? Ss 17:52 0:00 /usr/sbin/httpd

mysql 4447 94 12.8 2134672 1031064 ? Sl 10:52 27:39 /usr/libexec/mysqld

Quickly Tell If You Are on a 32 Bit or 64 Bit System

$ getconf LONG_BIT

If you're on a system and need to know if it's 32 or 64 bit, use getconf.

$ getconf LONG_BIT

$ ssh remote-host getconf LONG_BIT

Generate a Random Password

$ openssl rand -base64 48 | cut -c1-PASSWORD_LENGTH

$ gpw () { openssl rand -base64 48 | cut -c1-${1}; }

You can use the openssl command to generate a random password. If you find yourself doing this often, you can create a function. Simply pass in how long you want the password to be.

$ echo 'gpw () { openssl rand -base64 48 | cut -c1-${1}; }' >> ~/.bash_profile

$ . ~/.bash_profile

$ gpw

t3eyxkXBHAzb3VdR7G8NV3fMvZpXLOvT+AQwgQnw9pLm/UaRNHcPBjKaQsr26i3k

$ gpw 6

uu1ZMb