Operating system Linux What does "halt" mean? Linux command of "halt"
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Halt command in linux, descriptions and usage:


halt [options]

System administration command: turns off the computer. Insert a note in the file /var/log/wtmp; if the system is in runlevel 0 or 6, stop all processes; otherwise, call shutdown -h.



Suppress writing to /var/log/wtmp.


Call halt even when shutdown -nf would normally be called (i.e., force a call to halt, even when not in runlevel 0 or 6).


Place hard drives in standby mode before halt or power off.


Shut down network interfaces before halt.


No sync before reboot or halt.


Perform power-off when halting system.


Suppress normal call to sync.


Suppress normal execution; simply write to /var/log/wtmp.

You can see the following as a detail description and usage:

       halt, reboot, poweroff - stop the system.

       /sbin/halt [-n] [-w] [-d] [-f] [-i] [-p] [-h]
       /sbin/reboot [-n] [-w] [-d] [-f] [-i]
       /sbin/poweroff [-n] [-w] [-d] [-f] [-i] [-h]

       Halt  notes  that  the  system  is  being  brought  down  in  the  file  /var/log/wtmp, and then either tells the  kernel  to  halt,  reboot  or poweroff the system. If  halt or reboot is called when the system is not in runlevel 0 or 6, in other words when it`s running normally,  shutdown  will  be  invoked instead  (with  the  -h  or -r flag). For more info see the shutdown manpage.

       The rest of this manpage describes the behaviour in runlevels 0 and  6, that is when the systems shutdown scripts are being run.

       -n     Don`t sync before reboot or halt.

       -w     Don`t actually reboot or halt but only write the wtmp record (in
              the /var/log/wtmp file).

       -d     Don`t write the wtmp record. The -n flag implies -d.

       -f     Force halt or reboot, don`t call shutdown(8).

       -i     Shut down all network interfaces just before halt or reboot.

       -h     Put all harddrives on the system in  standby  mode  just  before
              halt or poweroff.

       -p     When halting the system, do a poweroff. This is the default when
              halt is called as poweroff.

       If you`re not the superuser, you will get the message must  be supe-ruser.

       Under  older sysvinit releases , reboot and halt should never be called directly. From release 2.74 on halt and reboot  invoke  shutdown if the system is not in runlevel 0 or 6. This means that if halt or reboot cannot find out the current runlevel (for example,  when  /var/run/utmp hasn`t been initialized correctly) shutdown will be called, which might not be what you want.  Use the -f flag if you want to do a hard halt or reboot.

       The  -h  flag  puts  all  harddisks in standby mode just before halt or poweroff. Right now this is only implemented for  IDE  drives.  A  side effect  of putting the drive in standby mode is that the write cache on the disk is flushed. This is important for IDE drives, since the kernel doesn`t flush the write-cache itself before poweroff.

       The halt program uses /proc/ide/hd* to find all IDE disk devices, which means that /proc needs to be mounted when halt or poweroff is called or the -h switch will do nothing.

Operating system - Linux