Issue 1045509: Problems with os.system and ulimit -f (original) (raw)

Created on 2004-10-12 15:34 by kowaltowski, last changed 2022-04-11 14:56 by admin. This issue is now closed.

Messages (5)
msg22654 - (view)	Author: Tomasz Kowaltowski (kowaltowski)	Date: 2004-10-12 15:34
Python version (running under Fedora Core 2 Linux): Python 2.3.3 (#1, May 7 2004, 10:31:40) [GCC 3.3.3 20040412 (Red Hat Linux 3.3.3-7)] on linux2 --------------------------------------------------------------------------- I found a problem while executing the 'ulimit -f' bash command within the 'os.system' function. According to the documentation this function should behave exactly like the stdlib function 'system'. However it does not happen as illustrated by the minimal Python and C examples: testsystem.py and testsystem.c (see attached zipped file). In these examples 'largefile' is a compiled C program which writes an endless file into the stdout (also attached). The C program testsystem.c works as expected and prints the following output: command: ulimit -f 10; largefile > xxx; result = 153 The Python program testsystem.py **does not stop**; if interrupted by Ctrl-C it prints: command: ulimit -f 10; largefile > xxx; result = 0 In both cases the output file 'xxx' has 10240 bytes, ie, 10 blocks as limited by 'ulimit'. It is interesting though that the command 'ulimit -t 1' (CPU time) produces correct results under both Python and C versions, ie, interrupts the execution and prints: command: ulimit -t 1; largefile > xxx; result = 137
msg22655 - (view)	Author: Tomasz Kowaltowski (kowaltowski)	Date: 2004-10-22 11:52
Logged In: YES user_id=185428 I also tested the new version "Python 2.4b1" -- the problem still occurs :-(.
msg22656 - (view)	Author: Gustavo Sverzut Barbieri (gsbarbieri)	Date: 2004-11-26 19:38
Logged In: YES user_id=511989 The problem is that python ignores the SIGXFSZ (File size limit exceeded) signal. import signal signal.signal( signal.SIGXFSZ, signal.SIG_DFL ) solves your problem. Any python developer: why does python ignores this signal?
msg22657 - (view)	Author: Neal Norwitz (nnorwitz) *	Date: 2005-10-03 06:35
Logged In: YES user_id=33168 It's set in Python/pythonrun.c. The reason is below. I'm not sure this can be changed. Any suggestions? I'd be happy to update doc, but have no idea where. revision 2.160 date: 2002/04/23 20:31:01; author: jhylton; state: Exp; lines: +3 -0 Ignore SIGXFSZ. The SIGXFSZ signal is sent when the maximum file size limit is exceeded (RLIMIT_FSIZE). Apparently, it is also sent when the 2GB file limit is reached on platforms without large file support. The default action for SIGXFSZ is to terminate the process and dump core. When it is ignored, the system call that caused the limit to be exceeded returns an error and sets errno to EFBIG. Python always checks errno on I/O syscalls, so there is nothing to do with the signal.
msg22658 - (view)	Author: Neal Norwitz (nnorwitz) *	Date: 2005-12-19 04:57
Logged In: YES user_id=33168 I don't know how to improve this, so closing.