Linux commands in brief

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pstree                                Processes and parent-child relarionships

top                                     Show top processes

ps -auxw                           process status

vmstat                               Monitor virtual memory

free                                   Display amount of free and used memory

in the system. (Also: cat /proc/meminfo)

map                                Display/examine memory map and

libraries (so). Usage: pmap pid

cat /proc/sys/vm/freepages

Display virtual memory “free pages”.

One may increase/decrease this limit:

echo 300 400 500 > /proc/sys/vm/freepages

uname -a                          print system information

cat /proc/version Display Linux kernel version in use.

cat /etc/redhat-release Display Red Hat Linux Release.

(also /etc/issue)

uptime                              Tell how long the system has been

running. Also number of users and

system’s load average.

w                                       Show who is logged on and what they are doing.

 /sbin/lsmod                       List all currently loaded kernel modules. Same as cat /proc/modules

/sbin/runlevel                   Displays the system’s current runlevel .

hostname                          Displays/changes the system’s nodename . (Must also manually change

hostname setting in /etc/sysconfig/network . Command will change entry in                                          /etc/hosts) service Display status of system services.

Example: service –status-all

Help: service –help

df -k                                  report filesystem disk space usage.

(-k reports in Kbytes)

du -sh                                Calculates file space usage for a given

directory. (and everything under it) (-s option summarizes)

mount                               Displays all mounted devices, their

mountpoint, filesystem, and access. Used

with command line arguments to mount file system.

cat /proc/filesystems Display filesystems currently in use.

cat /proc/mounts Display mounted filesystems currently in use.

showmount                      Displays mount info for NFS filesystems.

cat /proc/swaps Displays swap partition(s) size, type and

quantity used.

cat   /proc/ide/hda/anyfile

Displays disk information held by kernel.

who                                   Displays currently logged in users.

Use who -uH for idle time and terminal info.

users                                 Show all users logged in.

w                                       Displays currently logged in users and processes they are running.

whoami                             Displays user id.

 groups                              Display groups you are part of.

Use groups user-id to display groups for a given user.

set                                      Display all environment variables in your current environment.

id                                       Display user and all group ids. Use id user-id to display info for another user id.

last                                    Show listing of last logged in users.

history                              Shell command to display previously entered commands

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