Topic 8

Dates: 3/8/2017
Start-up and Run Levels. Scheduled jobs (at, cron)
Linux System Administration


System Run Levels (Legacy System V)


  • This is what used to be on older Linux distros.
    At bootup, init reads /etc/inittab file and executes all scripts for default run level. If the /etc/inittab is absent, the default run level is 2.
    On Unix, there are 7 conventional run levels (0,1,2,3,4,5,6). However, 10 levels are possible (0 -- 9).

  • On Ubuntu and Debian,
    
    Runlevel  0  - is halt.
    Runlevel  1  - is single-user.
    Runlevels 2-5  are multi-user.
    Runlevel  6  - is reboot.
    

  • On the other Linux systems, such as RedHat,
    
    Runlevel  0 - halt 
    Runlevel  1 - Single user mode
    Runlevel  2 - Multiuser, without NFS (The same as 3, if you do not have networking)
    Runlevel  3 - Full multiuser mode
    Runlevel  4 - unused
    Runlevel  5 - X11
    Runlevel  6 - reboot 
    

    File /etc/inittab specifies a default run level.
    
    # The default runlevel (2 in this  case).
    id:2:initdefault:
    
    If the /etc/inittab is absent, the default run level is 2.


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