Linux Essentials

RHCE 1:  Linux Essentials.  The following are the basic commands every newcomer to Linux should understand before building their repertoire on the way to becoming a Linux systems admin.

This post is logically the first in a series of posts to come, walking right around Linux, focussing on RedHat Enterprise Linux.

Connecting to a remote Linux System

telnet, ssh, rlogin

Listing the contents of a filesystem

ls -a     Show hidden files also

ls -F     Show file types i.e. / is a directory, * is a binary and @ is a symbolic link

ls -lh     Show a long listing (contains permissions etc in a human friendly format)

ls -ld     Show a long listing of directorys only (ignore files)

ls -R     Show listing, recursing into subdirectories (large output can be expected)

ls -t     Sort listing with newest first

ls -tr     Sort listing with oldest first (reverse)

List users on the system

w     The what command.  Displays detailed user info like a combination of who and top for the specified user account

who     Display logged in users

who am i     Display info about your logged in user account who executed the command

whoami     Display your username

logname     Show the real username of logged in user (e.g. is su or sudo to another user account)

tty     Display pseudo terminal that you’re logged into e.g /dev/pts/1

id     Display UID for your user account (and gid)

groups     Display groups your user account is a member of

Display information about the system

uname     Display information about the operating system

-a -s -n -r -v -m -p -i -o

hostname     Display hostname of the system (also used to set hostname)

date     Displays time and date

/sbin/hwclock     Display and set hardware clock

cal     Display month calendar

uptime     Display current time elapsed since initial booting, number of users logged in and load averages

top     Display top running processes, Shift + M to sort my memory instead of CPU

Display information about commands

which     Display the absolute path to the specified binary executed, e.g. which cat gives /bin/cat

whereis     Display location of binary and location of man pages for specified binary

man     Display manual page for specified command

man 1     Display user commands section of man page for specified command

man 4     Display special files section of man page for specified command

man 5    Display system configuration files section of man page for a given command

man -k or apropos     Displays man pages sections pertinent to specified search keyword

passwd –help or passwd -?     Displays quick help for passwd command or other command

whatis  or man -f   Displays description for config file or binary, e.g. whatis yum.conf gives Config file for yum package mgmt system

 

 

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