.TH "timeout" 1 "5 June 2011" "Mark Wooding" "Toys"
.SH NAME
timeout \- run a program for at most a given amount of time
.
.SH SYNOPSIS
.B timeout
.RB [ \-s
.IR signal ]
.I seconds
.I command
.RI [ arguments ...]
.
.SH DESCRIPTION
The
.B timeout
command runs a specified program for at most a given number of
.IR seconds .
.PP
It works by running the given command as a separate process group.  It
then waits either for the top-level process (only) to exit, or for the
timeout to expire, whichever happens first.  If the process exits, then
.B timeout
exits too, setting its exit status to match.  Any other processes which
may have been started are left unmolested.
.PP
On the other hand, if the timeout goes off, then
.B timeout
sends its child process group the specified signal, by default
.BR SIGTERM ,
though you can choose a different one with the
.B \-s
option.  It then waits an additional five seconds.  If the child still
hasn't exited, it sends
.B SIGKILL
to the process group and waits a further five seconds.  If the child
still hasn't exited in this time, then
.B timeout
gives up and exits.
.PP
The following command-line options are recognized.
.TP
.B \-h, \-\-help
Prints a reasonably full help message describing the arguments and
options to standard output, and exits successfully.
.TP
.B \-v, \-\-version
Prints the program's version number to standard output, and exits
successfully.
.TP
.B \-u, \-\-usage
Prints a brief usage summary to standard output, and exits successfully.
.TP
.BI "\-s, \-\-signal=" signal
Send
.I signal
to the child process if it takes too long.  The default is to send
.BR SIGTERM .
A signal may be given numerically (e.g., 9 for
.BR SIGKILL )
or by name (e.g.,
.BR KILL ).
.
.SH BUGS
Because
.B timeout
works by running its child process in a separate process group, it
interacts oddly with interactive shells.  If the child process group
attempts to do terminal I/O (particularly reading from a terminal) then
it may be sent signals to suspend it.  This may or may not make matters
worse.
.PP
The
.B timeout
program makes an effort to propagate interesting signals to its child
process group.  Currently, it propagates
.BR SIGTSTP ,
.BR SIGCONT ,
.BR SIGINT ,
.BR SIGHUP ,
and
.BR SIGQUIT .
This list is subject to change: I don't think I'm likely to remove any
of the current signals from it, but I might add some; or I might add an
option to control this list.
.PP
If you suspend
.B timeout
and its child process group, the timer continues running anyway.  (I'm
not quite sure whether this is the right behaviour.)
.PP
Nested timeouts don't work in a useful way if the outer timeout expires
earlier than the inner one.  Since
.B SIGTERM
isn't propagated (currently, at least), the inner
.B timeout
is killed by the outer one, and loses control of its child process
group.  You could possibly work around this by sending
.B SIGQUIT
instead.
.PP
Perhaps it would be useful to allow configuration of the `panic'
timeouts after the initial timeout signal is sent.
.
.SH AUTHOR
Mark Wooding, <mdw@distorted.org.uk>