Strange behavior redirecting to a file while using runuser

Question

I'm currently executing a python file with runuser and redirecting the output to a file. This is the command:

runuser -l "user" -c "/path/python-script.py parameter1 > /path/file.log &"

This run correctly the python script but creates an empty log file. If I run without the redirect:

runuser -l "user" -c "/path/python-script.py parameter1 &"

runs correctly the python script and make all output from python script to flow the screen. The output from the python script are done with print which output to stdout.

I don't understand why the output from the python script is not dumped to the file. File permissions are correct. The log files is created, but not filled.

But, if I remove the "parameter1", then the error message reported by the python script is correctly dumped to the log file:

runuser -l "user" -c "/path/python-script.py > /path/file.log &"

The error message is done with print too, so I don't understand why one message are dumped and others not.

Maybe runuser interprets the "parameter1" as a command or something. But, the parameter is correctly passed to the script, as I can see with ps:

/usr/bin/python /path/python-script.py connect

I've tried adding 2>&1 but still don't work.

Any idea ?

Does the python script terminate on error and continue running until you kill it otherwise? Then buffering may be the cause (then try python -u /path/python-script.py > /path/file.log &). — Anton Kovalenko
– Anton Kovalenko, Commented Feb 12, 2013 at 13:01

Mario Barcz · Accepted Answer · 2013-09-18 08:37:35Z

0

Encountered similar problem in startup scripts, where I needed to log output. In the end I came up with following:

USR=myuser    
PRG=myprogrog
WKD="/path/to/workdir"
BIN="/path/to/binary"
ARG="--my arguments"
PID="/var/run/myapp/myprog.pid"

su -l $USR -s /bin/bash -c "exec > >( logger -t $PRG ) 2>&1 ; cd $WKD; { $BIN $ARG & }; echo \$! > $PID "

Handy as you can also have PID of the process available. Example writes to syslog, but if it is to write to the file use cat:

LOG="/path/to/file.log"

su -l $USR -s /bin/bash -c "exec > >( cat > $LOG ) 2>&1 ; cd $WKD; { $BIN $ARG & }; echo \$! > $PID "

It starts a new shell and ties all outputs to command inside exec.

answered Sep 18, 2013 at 8:37

Mario Barcz

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