lfs-book/appendixa/sysvinit-desc.xml

<sect2><title>Short descriptions</title>

<para><command>halt</command> normally invokes shutdown with the -h flag,
except when already in runlevel 0, then it tells the kernel to halt the system.
But first it notes in the file <filename>/var/log/wtmp</filename> that the
system is being brought down.</para>

<para><command>init</command> is the mother of all processes. It reads its
commands from <filename>/etc/inittab</filename>, which normally tell it which
scripts to run for which runlevel, and how many gettys to spawn.</para>

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

<para><command>last</command> shows which users last logged in (and out),
searching back through the file <filename>/var/log/wtmp</filename>. It can
also show system boots and shutdowns, and runlevel changes.</para>

<para><command>lastb</command> shows the failed login attempts, as logged
in <filename>/var/log/btmp</filename>.</para>

<para><command>mesg</command> controls whether other users can send
messages to the current user's terminal.</para>

<para><command>pidof</command> reports the PIDs of the given programs.</para>

<para><command>poweroff</command> tells the kernel to halt the system and
switch off the computer. But see halt.</para>

<para><command>reboot</command> tells the kernel to reboot the system.
But see halt.</para>

<para><command>runlevel</command> reports the previous and the current
runlevel, as noted in the last runlevel record in
<filename>/var/run/utmp</filename>.</para>

<para><command>shutdown</command> brings the system down in a secure way,
signaling all processes and notifying all logged-in users.</para>

<para><command>sulogin</command> allows the superuser to log in. It is
normally invoked by init when the system goes into single user mode.</para>

<para><command>telinit</command> tells init which runlevel to enter.</para>

<para><command>utmpdump</command> displays the content of the given login
file in a friendlier format.</para>

<para><command>wall</command> writes a message to all logged-in users.</para>

</sect2>