1) useradd = create a new user or updates default new user information

Usage:

useradd login options

Examples:

# useradd usr1 — Add new user usr1 with default settings

# useradd usr1 -d /home/usr1 — Create the new user’s home dir in /home

# useradd usr1 -e 2009-04-30 — From 30/4/2009 the user acc will be disabled.

# useradd usr1 -f 6 — After passwd expires, system will allow the user to login for 6 days with a warning to change his passwd.

# useradd usr1 -g staff — Set user1 group as staff

# useradd usr1 -p $1$d8 — Create the usr1 with the given encrypted password. For No passwd, acc disabled.

# useradd usr1 -s /bin/csh — Set C Shell as the default login shell for the usr1

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2) userdel = delete a user account and user’s related filesĀ 

userdel loginname – delete the user account

userdel -r loginname - delete the user account together with user’s home directory and all files inside it

userdel -f loginname – for the deletion even the user is still log in, it will force to delete the user’s home directory and files as well, this option is dangerous use with caution

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3) usermod = to modify a users account

Examples:

# usermod -d /home2/usr1 usr1 — Create the new home Dir for usr1 in /home2 & Move old Dir contents to this Dir.

# usermod -e 2005-04-30 usr1 — From 30/4/2005 the usr1 acc will be disabled.

# usermod -f 6 usr1 — After passwd expires, system will allow the user to login for 6 days with a warning to change his passwd.

# usermod -g prof usr1
— Set usr1′s initial group as prof.

# usermod -p $1$d8 usr1 — Set the new passwd for the usr1

# usermod -s /bin/bash usr1 — Set Bash as the default login shell for the usr1.

# usermod -L usr1 — Lock a user’s password.

# usermod -U usr1 — Unlock a user’s password.

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4) groupadd = create a new group

# groupadd sales

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5) last = show listing of last logged in usersĀ 

Examples:

$ last — List all entries.

$ last tty6 — List, who are all logged thru tty6.

$ last bharathi — List all entries of bharathi (user).

$ last -6 — List only last 6 entries.

$ last -R
— Don’t show the Host Name field in output.

$ last -a – Show Host Name field in last column.

$ last -i – Show IP Number for Remote host.

$ last -t 20080818120000 — List all entries upto Aug 18 12:00:00 2008

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6) lastb = display a list of recent bad login attempts (from the /var/log/btmp file). Accepts the same option flags and arguments as last


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