Red Hat Bugzilla – Bug 504926
possible expect fd leak when spawn
Last modified: 2009-09-21 11:10:32 EDT
Description of problem: It seems that spawn has fd leak with /dev/null, as illustrated by example code. If you see the example code is invalid, feel free to close this bug. Version-Release number of selected component (if applicable): expect-5.43.0-15.fc10.x86_64 How reproducible: always Steps to Reproduce: 1. create t.tcl with this content: #!/usr/bin/expect while (1) { spawn sleep 1 expect eof {} } 2. run t.tcl 3. in another terminal, run ls -l /proc/$(pgrep t.tcl)/fd Actual results: The number of fd grows one per second. Eventually the script dies after running out of fd. Expected results: The number of fd should be bounded. Additional info: n/a
Hi, The code is invalid. Actually, you are creating zombie process every single second. Run your script and see output of "ps aux": 14310 pts/1 S+ 0:00 /usr/bin/expect ./t.tcl 14312 ? Zs 0:00 [sleep] <defunct> 14316 ? Zs 0:00 [sleep] <defunct> 14320 ? Zs 0:00 [sleep] <defunct> 14325 ? Zs 0:00 [sleep] <defunct> 14330 ? Zs 0:00 [sleep] <defunct> ... You should reap the sleep processes - modify your script to: #!/usr/bin/expect while {1} { spawn sleep 1 expect eof {} wait } Check "ps aux" and "ls -l /proc/$(pgrep t.tcl)/fd" - looks better, right?;)
Vitezslav, Thanks for pointing my user error! Good, so there is no bug. I wondered if we can add this to 'man expect', somewhere around the 'spawn' command, that one needs to use 'wait' to reap the spawned process.
Well, it's mentioned near the 'close' command in man page: "No matter whether the connection is closed implicitly or explicitly, you should call wait to clear up the corresponding kernel process slot. close does not call wait since there is no guarantee that closing a process connection will cause it to exit. See wait below for more info." Of course, when the script is finished, everything is reaped automatically. But the man page is meant primarily as reference material. If you need/want to learn how to use Expect effectively and in full range, I recommend you the book written by author of Expect Don Libes - "Exploring Expect".
Vitezslav, Thanks for info! Understand now.