lfs-book/appendixa/sysvinit-desc.xml

<sect2>
<title>Contents</title>

<para>
The Sysvinit package contains the pidof, last, lastb, mesg, utmpdump,
wall, halt, init, killall5, poweroff, reboot, runlevel, shutdown,
sulogin and telinit programs.
</para>

</sect2>

<sect2><title>Description</title>

<sect3><title>pidof</title>

<para>
Pidof finds the process id's (pids) of the named programs and prints
those id's on standard output.
</para>

</sect3>

<sect3><title>last</title>

<para>
last searches back through the file /var/log/wtmp (or the file designated 
by the -f flag) and displays a list of all users logged in (and  out) 
since that file was created.
</para>

</sect3>

<sect3><title>lastb</title>

<para>
lastb is the same as last, except that by default it shows a log of the 
file /var/log/btmp, which contains all the bad login attempts.

</para>

</sect3>

<sect3><title>mesg</title>

<para>
Mesg controls the access to the users terminal by others. It's typically 
used to allow or disallow other users to write to his terminal.
</para>

</sect3>

<sect3><title>utmpdump</title>

<para>
utmpdumps prints the content of a file (usually /var/run/utmp) on
standard output in a user friendly format.
</para>

</sect3>

<sect3><title>wall</title>

<para>
Wall sends a message to everybody logged in with their mesg permission 
set to yes.
</para>

</sect3>

<sect3><title>halt</title>

<para>
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, shutdown will be invoked instead (with the flag -h or -r).
</para>

</sect3>

<sect3><title>init</title>

<para>
Init is the parent of all processes. Its primary role is to create 
processes from  a  script  stored  in  the  file /etc/inittab. This  
file usually has entries which cause init to spawn gettys on each line that
users can log in. It also controls autonomous processes required by any 
particular system.
</para>

</sect3>

<sect3><title>killall5</title>

<para>
killall5 is the SystemV killall command. It sends a signal to all 
processes except the processes in its own session, so it won't kill the 
shell that is running the script it was called from.
</para>

</sect3>

<sect3><title>poweroff</title>

<para>
poweroff is equivalent to shutdown -h -p now. It halts the computer and
switches off the computer (when using an APM compliant BIOS and APM is 
enabled in the kernel).
</para>

</sect3>

<sect3><title>reboot</title>

<para>
reboot is equivalent to shutdown -r now. It reboots the computer.
</para>

</sect3>

<sect3><title>runlevel</title>

<para>
Runlevel reads the system utmp file (typically /var/run/utmp) to locate 
the runlevel record, and then prints the previous and current system 
runlevel on its standard  output, separated by a single space.
</para>

</sect3>

<sect3><title>shutdown</title>

<para>
shutdown brings the system down in a secure way. All logged-in users are 
notified that the system is going down, and login is blocked.
</para>

</sect3>

<sect3><title>sulogin</title>

<para>
sulogin is invoked by init when the system goes into single user mode 
(this is done through an entry in /etc/inittab). Init also tries to 
execute sulogin when it is passed the -b flag from the boot loader (eg, LILO).
</para>

</sect3>

<sect3><title>telinit</title>

<para>
telinit sends appropriate signals to init, telling it which runlevel to
change to.
</para>

</sect3>

</sect2>