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What Linux run level am I in?

Linux / Unix systems have a "run level" that they're in ...
0 - halted
1 - single user
2 - multiuser (client)
3 - full multiuser
5 - full multiuser with X windows running
6 - reboot

How do I find out what run level a system is in at the moment? - a question asked on today's Java course (OK - it was over lunch and we were a bit a lot off topic ...)


1. The runlevel command tells you what run level you are in

2. The who -r command also tells you the run level, together with some other information.

Here's a machine which is in full multiuser mode, running as a server:

[trainee@melksham ~]$ /sbin/runlevel
N 3
[trainee@melksham ~]$ who -r
run-level 3 2009-05-15 09:28 last=S
[trainee@melksham ~]$


And here's one which is in full multiuser mode and has the windows system running too ...

[trainee@easterton ~]$ /sbin/runlevel
N 5
[trainee@easterton ~]$ who -r
run-level 5 2009-05-15 15:04 last=S
[trainee@easterton ~]$


Notes:

1. The runlevel command is intended for administrators only, so is in the sbin directory which is not on the normal user's path. However, the command is purely information so is available to all users who know where to find it.

2. The default run level of a system can be changed by updating the /etc/inittab file ... the line
id:5:initdefault:
will bring the system up into run state 5 on startup / reboot. Change the 5 to a 3 if you want the machine to start / reboot into run state 3

3. It is strongly recommended that you do not run your web servers in run state 5 ... I have had instances on a course where delegates have complained about a slow server, and they have been amazed when I have walked up to a 'spare' machine, moved the mouse around, and asked if the performance has improved. They have been even more amazed to be able to confirm that it HAS made a difference. What had happened? The system was running a screen saver in X Windows ... and it was eating up all the cpu resource in keeping an "atlantis" display of 3D whales and sharks swimming around the screen. Moving the mouse cancelled the screen saver ... and released the resources back to the server

4. Rather obviously, runlevel cannot report that a machine is in run state 0!
(written 2009-05-15)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
A164 - Web Application Deployment - Services and Regular Jobs
  [4487] Starting MySQL. ERROR! The server quit without updating PID file - how we fixed it. - (2015-05-06)
  [3792] Managing daemons from a terminal session - (2012-07-01)
  [3791] The Kernel, Shells and Daemons. Greek Gods in computing - (2012-07-01)
  [3143] On time - (2011-01-23)
  [3011] What are .pid files? - (2010-10-23)
  [2145] Using the internet to remotely check for power failure at home (PHP) - (2009-04-29)
  [1903] daemons - what is running on my Linux server? - (2008-11-23)
  [1765] Dialects of English and Unix - (2008-08-21)
  [1733] memcached - overview, installation, example of use in PHP - (2008-08-02)
  [1731] Apache httpd, MySQL, PHP - installation procedure - (2008-08-01)
  [1700] FTP server on Fedora Linux - (2008-07-06)
  [1633] Changing a screen saver from a web page (PHP, Perl, OSX) - (2008-05-06)
  [1553] Automatic startup and shutdown of Tomcat - (2008-02-24)
  [1288] Linux run states, shell special commands, and directory structures - (2007-08-03)
  [1028] Linux / Unix - process priority and nice - (2007-01-10)
  [907] Browser -> httpd -> Tomcat -> MySQL. Restarting. - (2006-10-28)
  [544] Repeating tasks with crontab - (2005-12-27)


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