Detect Command Timeouts using Bash

 A common, and often overlooked, need for scripting is addressing hanging, or unresponsive commands.  What should your script do if one of it's ste

ps takes much, much, much longer than expected?  A hanging, or unresponsive, subprocess will result in a hanging job which in turn can prevent oth

er jobs from running.  Let's spend a bit of time how to address such an need.

 

The 'timeout' command is provided by the coreutils package, often readily available on default installation for most distributions.

 

$ sleep 10

$ echo $?

0

 

Execution of subprocesses generally set a return code, zero or non-zero, often zero indicating successful execution of the command, non-zero return codes if it failed for some reason.  The above command sequence will execute a sleep command (for 10 seconds), the second command echoing the return code.  Assignment of $? to zero indicates the sleep command executed successfully.

 

So, what if we wanted to prevent a hanging command to go undetected and/or prevent the rest of a script from running.  Let's say we want to enforce a command takes no longer than 5 seconds.
 

$ timeout 5 sleep 10

$ echo $?

124

 

After 5 seconds, the command terminates, the return code 124 indicates the command timed out.  Usage of this allows setting hard constraints on how long a command is allowed to run before terminating or being terminated.  The return code allows determining if the command timed-out.
 

Cheers.