who command is used to find out the following information :
1. Time of last system boot
2. Current run level of the system
3. List of logged in users and more.
Description : The who command is used to get information about currently logged in user on to system.
Syntax : $who [options] [filename]
Examples :
1. The who command displays the following information for each user currently logged in to the system if no option is provided :
- Login name of the users
- Terminal line numbers
- Login time of the users in to system
- Remote host name of the user
hduser@mahesh-Inspiron-3543:~$ who hduser tty7 2018-03-18 19:08 (:0) hduser@mahesh-Inspiron-3543:~$
2. To display host name and user associated with standard input such as keyboard
hduser@mahesh-Inspiron-3543:~$ who -m -H NAME LINE TIME COMMENT
3. To show all active processes which are spawned by INIT process
hduser@mahesh-Inspiron-3543:~$ who -p -H NAME LINE TIME PID COMMENT
4. To show status of the users message as +, – or ?
hduser@mahesh-Inspiron-3543:~$ who -T -H NAME LINE TIME COMMENT hduser + tty7 2018-03-18 19:08 (:0)
5. To show list of users logged in to system
hduser@mahesh-Inspiron-3543:~$ who -u hduser tty7 2018-03-18 19:08 01:16 3357 (:0)
6. To show time of the system when it booted last time
hduser@mahesh-Inspiron-3543:~$ who -b -H
NAME LINE TIME PID COMMENT
system boot 2018-03-18 19:07
7. To show details of all dead processes
hduser@mahesh-Inspiron-3543:~$ who -d -H (NO dead process in this case) NAME LINE TIME IDLE PID COMMENT EXIT NAME LINE TIME IDLE PID COMMENT EXIT
8. To show system login process details
hduser@mahesh-Inspiron-3543:~$ who -l -H NAME LINE TIME IDLE PID COMMENT LOGIN tty1 2018-03-18 19:07 3073 id=tty1
9. To count number of users logged on to system
hduser@mahesh-Inspiron-3543:~$ who -q -H hduser # users=1
10. To display current run level of the system
hduser@mahesh-Inspiron-3543:~$ who -r
run-level 5 2018-03-18 19:07
11. To display all details of current logged in user
hduser@mahesh-Inspiron-3543:~$ who -a
system boot 2018-03-18 19:07
LOGIN tty1 2018-03-18 19:07 3073 id=tty1
run-level 5 2018-03-18 19:07
hduser + tty7 2018-03-18 19:08 01:13 3357 (:0)
12. To display system’s username
hduser@mahesh-Inspiron-3543:~$ whoami hduser
13. To display list of users and their activities
hduser@mahesh-Inspiron-3543:~$ w 20:39:20 up 1:32, 1 user, load average: 0.09, 0.06, 0.07 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT hduser tty7 :0 19:08 1:32m 38.95s 0.19s /sbin/upstart -
14. To display user identification information
hduser@mahesh-Inspiron-3543:~$ id uid=1001(hduser) gid=1001(hadoop) groups=1001(hadoop), 27(sudo)
Note : For more details, refer linux man page.
