Experimental Physics and
Industrial Control System

"Vodopivec, Klemen via Tech-talk" <tech-talk at aps.anl.gov> · Thu, 22 Jul 2021 13:02:28 +0000

Hi,

This may be loosely related to EPICS, but since it’s only happening with caget/pvget commands I thought to ask here.

We’ve been having a weird issue when querying for a PV value from a BASH script. Most of the time the script works and is run several times in a day. Occasionally it will stop working. Debugging the script with bash -x, the last line is always:

remexp_enabled=$(pvget -p ca -w 0.5 -t ${BL}:CS:TL:RemExp:En 2>/dev/null)

After that line, the bash script simply freezes and has to be terminated. pvget replaced caget, giving us two implementations that behave the same. There are several grep and other commands before this line which execute just fine, which eliminates the obvious out-of-resources issue. Capturing network traffic with Wireshark shows that pvget completes the request and closes the socket just fine.

Interestingly, adding a dummy redundant pvget beforehand fixes the issue for the duration of the script:

pvget -p ca -w 0.5 -t ${BL}:CS:TL:RemExp:En 2>/dev/null
remexp_enabled=$(pvget -p ca -w 0.5 -t ${BL}:CS:TL:RemExp:En 2>/dev/null)

However, when similar dummy pvget is run before executing the script, the issue gets resolves completely.

Any ideas how to troubleshoot are much welcome.

Thanks, Klemen

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System