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Looking in my /etc/inittab file I see the following entry:

ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now

What do the -t1 and -a options mean? They do not appear in the manual for the shutdown command. I have also seen another /etc/inittab in a reference book that shows:

ca::ctrlaltdel:/sbin/shutdown -r -t 4 now

Since no runlevel is specified, does this mean that it is works for all run levels from 0 to 6? What does the "-t 4" mean?

Also, is there a reason why the -a and -t options are not mentioned in the manual for the shutdown command?

kojow7
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  • As noted in one of the answers you are probably, given what you say, using an operating system where [`/etc/inittab` is a thing of the past](http://jdebp.eu./FGA/inittab-is-history.html), so what it contains is entirely irrelevant to the actual operation of your machine. See https://unix.stackexchange.com/a/394238/5132 and what it hyperlinks to for more. – JdeBP Feb 09 '18 at 05:32

1 Answers1

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Those options are options to the sysvinit version of shutdown (see the relevant manpage):

-t sec

Tell init(8) to wait sec seconds between sending processes the warning and the kill signal, before changing to another runlevel.

-a

Use /etc/shutdown.allow.

This version of -t is also valid in your second example, which as you guess applies to any runlevel.

The options are no longer mentioned in your version of the manual because that’s no doubt the systemd version, which doesn’t support them.

Community
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Stephen Kitt
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  • … and which totally ignores `/etc/inittab` in any case. [Upstart's `shutdown` manual page](http://manpages.ubuntu.com/manpages/xenial/en/man8/shutdown.8.html) does not mention these, either. Upstart does not use `/etc/inittab` either and unlike systemd has [a manual page saying that](http://manpages.ubuntu.com/manpages/xenial/en/man5/inittab.5.html) – JdeBP Feb 09 '18 at 05:23