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I'm writing a mock-grading script in bash. It's supposed to execute a C program which will give some output (which I redirect to a file.) I'm trying to (1) make it timeout after a certain duration and also (2) terminate if the output file reaches a certain file size limit. Not sure how to go about either of these. Any help? Thanks.

Chris
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3 Answers3

3

There's a GNU coreutil command timeout to do timeouts.

Investigate ulimit -f 32 to set the maximum file size (to 16 KiB; it counts in 512 byte blocks).

Objection:

ulimit is [not] suitable because I have to create other files as well. I need to limit only one of them.

Counter: Unless the program must create a big file and a little file and you have to limit just the little file, you can use a sub-shell to good effect:

(
ulimit -f 32
timeout 10m -- command arg >file
)

The limit on file size is restricted to the commands in the sub-shell (which is marked by the pair of parentheses).

Jonathan Leffler
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  • I don't think ulimit is suitable because I have to create other files as well. I need to limit only one of them. – Chris Apr 13 '10 at 04:00
  • This solution works well for the file limit condition. However, I can't use the coreutils (the machines this has to run on don't have them installed.) Is there another option for timeout? – Chris Apr 13 '10 at 04:20
  • @Chris, you could start another script in the background that sleeps nnn seconds and then sends a signal to the parent PID, which the parent could handle with `trap`. Racey, but it should work. – Tim Post Apr 13 '10 at 04:32
  • GNU coreutils are things like 'ls' - and current versions of coreutils (8.4 verified present; 6.12 verified absent) contain `timeout`. – Jonathan Leffler Apr 13 '10 at 04:50
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you can use timeout command eg

timeout -s 9 5s ./c_program > file

to check file size, you can stat the file, then do if/else

limit=1234 #bytes
size=$(stat -c "%s" file)
if [ "$size"  -gt "$limit" ] ;then
  exit
fi

see also here if you can't use these GNU tools, or here for some other inspirations.

Community
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ghostdog74
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This starts yourcommand, redirecting output via dd to youroutputfile and putting a limit of 10000000 bytes on it: dd will terminate and SIGPIPE will be sent to yourcommand

yourcommand | dd of=youroutputfile bs=1 count=10000000 &

This will wait 5 seconds and kill yourcommand if not already terminated:

sleep 5
kill %yourcommand
Jürgen Hötzel
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