为程序设置超时

timeout 是个奇妙的Linux命令，它可以控制程序运行的时间，这对于我们希望控制程序的运行时间非常有用。

timeout在CentOS 6平台上，从属于软件包coreutils

# which timeout
/usr/bin/timeout
# rpm -qf /usr/bin/timeout
coreutils-8.4-19.el6_4.2.x86_64

timeout的原理很简单，一个简单的计时器，一个kill命令，其中-s 可以跟kill的参数，具体怎么杀，就看它。

man timeout仅仅半页，如下

TIMEOUT(1)                       User Commands                      TIMEOUT(1)
NAME
       timeout - run a command with a time limit
SYNOPSIS
       timeout [OPTION] NUMBER[SUFFIX] COMMAND [ARG]...
       timeout [OPTION]
DESCRIPTION
       Start  COMMAND,  and kill it if still running after NUMBER seconds.  SUFFIX may be ‘s’ for seconds (the default), ‘m’ for minutes, ‘h’
       for hours or ‘d’ for days.
       Mandatory arguments to long options are mandatory for short options too.
       -s, --signal=SIGNAL
              specify the signal to be sent on timeout.  SIGNAL may be a name like ‘HUP’ or a number.  See ‘kill -l‘ for a list of signals
       --help display this help and exit
       --version
              output version information and exit
       If the command times out, then exit with status 124.  Otherwise, exit with the status of COMMAND.  If no signal is specified, send the
       TERM signal upon timeout.  The TERM signal kills any process that does not block or catch that signal.  For other processes, it may be
       necessary to use the KILL (9) signal, since this signal cannot be caught.
AUTHOR
       Written by Padraig Brady.

用法举例

timeout 120 command

上面的command命令如果在120秒内完成，则平安结束，运行超过120秒后将被杀死。

脚本经常是傻乎乎的一口气跑到完，搞得我们需要写另一个脚本定期去杀它。自打有了timeout命令，腰也不疼了，腿也不酸了，跑跑歇歇更健康。

一句话，我们在脚本里或者crontab里就不用再造轮子了。