How to see which users are logged in on OS X and Linux

There are two funky commands that can help us see who’s currently logged in, and what operations were performed last. Those two commands are who and last.

Let me show you how to use them.

The who command

Type who at the command prompt and you’ll see a list of currently logged-in users:

who

versluis tty1         2015-11-19 11:21 (:0)
root     pts/0        2015-11-19 11:46 (10.0.1.55)

This system has two users logged in: versluis, via TTY, and root via PTS. We also get to see which IP addresses these users are logged in from (:0 is localhost).

On this note, TTY is the local text based terminal at the machine, while PTS is a pseudo-terminal. This is most likely an SSH session or similar, anything that’s happening remotely.

who can also show us who we are, in case you’re ever logged in on a system and don’t know which user you are:

who am i

your-username-here

You can also concatenate who am i into whoami.

The last command

The last command can take a moment to execute and will show a list similar to this:

last

versluis tty1         :0               Tue Feb 10 18:54 - down  (4+13:11)   
reboot   system boot  2.6.32-504.8.1.e Tue Feb 10 18:51 - 08:05 (4+13:14)   
root     pts/1        10.0.1.43        Tue Feb 10 16:33 - 16:44  (00:10)    
root     pts/0        10.0.1.52        Tue Feb 10 11:36 - down   (07:13)    
versluis pts/0        :0.0             Tue Feb 10 11:35 - 11:35  (00:00)    
versluis tty1         :0               Tue Feb 10 11:29 - down   (07:20)    
reboot   system boot  2.6.32-504.8.1.e Tue Feb 10 11:27 - 18:50  (07:22)    
root     tty1                          Tue Feb 10 11:16 - down   (00:09)    
reboot   system boot  2.6.32-504.8.1.e Tue Feb 10 11:15 - 11:25  (00:10)    
reboot   system boot  2.6.32-504.8.1.e Tue Feb 10 10:59 - 11:25  (00:26)    
root     tty1                          Tue Feb 10 10:29 - down   (00:28)    
reboot   system boot  2.6.32-504.el6.i Tue Feb 10 10:28 - 10:58  (00:29)    

wtmp begins Tue Feb 10 10:28:53 2015

You can see who has logged in to the system recently, from which IP address, and when each session started and finished. You can also see when the system was last restarted (and in Linux, which Kernel was used to do so).

The last line (on Linux, beginning with wtmp) shows since when the command was able to display results. last and who both read a file called wtmp (in /var/log/wtmp), which logs all login attempts over time.

last accepts several filtering options too. For example, to query when a particular user has logged on and off, type last followed by the username:

last versluis

versluis tty1         :0               Thu Nov 19 11:21   still logged in   
versluis tty1         :0               Tue Nov 17 12:44 - 22:32  (09:48)    
versluis tty1         :0               Tue Nov 17 11:13 - down   (01:29)    
versluis tty1         :0               Sat Oct 31 23:35 - crash (16+12:37)  
versluis tty1         :0               Sun Aug  9 09:09 - down  (83+14:24)  
versluis tty1         :0               Tue Jun 30 18:03 - down  (39+15:04)  
versluis pts/0        10.0.1.52        Thu Feb 19 14:41 - 18:34  (03:52)

Or if you’re only interested in restarts:

last reboot

reboot   system boot  2.6.32-573.8.1.e Thu Nov 19 11:20 - 12:02  (00:41)    
reboot   system boot  2.6.32-573.8.1.e Tue Nov 17 12:43 - 12:02 (1+23:18)   
reboot   system boot  2.6.32-573.7.1.e Tue Nov 17 11:12 - 12:42  (01:29)    
reboot   system boot  2.6.32-573.7.1.e Sat Oct 31 23:34 - 12:42 (16+14:07)  
reboot   system boot  2.6.32-573.1.1.e Sun Aug  9 09:08 - 23:33 (83+14:24)  
reboot   system boot  2.6.32-504.23.4. Tue Jun 30 18:02 - 09:07 (39+15:05)  
reboot   system boot  2.6.32-504.8.1.e Sun Feb 15 11:30 - 09:07 (174+20:37) 

On OS X the output is somewhat more limited due to the absence of kernels, but it works just the same. For more information on each command, checkout the man pages with man last and man who.





Jay is the CEO and founder of WP Hosting, a boutique style managed WordPress hosting and support service. He has been working with Plesk since version 9 and is a qualified Parallels Automation Professional. In his spare time he likes to develop iOS apps and WordPress plugins, or draw on tablet devices. He blogs about his coding journey at http://wpguru.co.uk and http://pinkstone.co.uk.