[problem]
You want to know who is on the system. Or which userid you are using.
 What runlevel you are at – or when the system was booted.
All doable with who.
[/problem]
[solution]
See the example and reference tabs, to see 5 ways to run who, showing different things about the system and users.
[/solution]
[example]
1. Basic
 [marcus@bagend puterpet]$ who
 marcus   pts/1        Sep 19 16:07 (10.0.0.8)
 marcus   pts/3        Sep 22 17:46 (10.0.0.8)
 
2. With Heading and Idle time dot means currently active.
 [marcus@bagend puterpet]$ who  -Hu
 NAME     LINE         TIME         IDLE          PID COMMENT
 marcus   pts/1        Sep 19 16:07   ?         29984 (10.0.0.8)
 marcus   pts/3        Sep 22 17:46   .         29566 (10.0.0.8)
 
3. Show who I am in the current shell and where I came from.
 [marcus@bagend puterpet]$ who am i
 marcus   pts/3        Sep 22 17:46 (10.0.0.8)
 
4. Show the current run level Shows boot time and last runlevel too.
 [marcus@bagend puterpet]$ who -r
          run-level 5  Sep  9 10:47                   last=S
 
5. Show last boot time
 [marcus@bagend puterpet]$ who -b
          system boot  Sep  9 10:47
 
[/example]
[reference]
[tags]who command, Unix Coding School[/tags]
[/reference]
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