0fc2f7a7_torial___A_Beginner_s_handbook__Meaning
[System Variable] TMOUT [To View Variable Value Type] echo $TMOUT [Meaning] 
The default timeout for the read builtin command. Also in an interactive shell, the value is interpreted as the number of seconds to wait for input after issuing the command. If not input provided it will logout user.
Variables - Linux Shell Scripting Tutorial - A Beginner's handbook
Meaning