How to find which IOC provides a PV

Tags: beginner user developer

This process is for IOCs running on Linux servers.

Find Host and TCP port

The cainfo command will tell you which host is serving a particular PV, and which TCP port number on that host is used.

$ cainfo LN-TS{EVR:1A-SFP}Pwr:RX-I
State:            connected
Access:           read, write
Native data type: DBF_DOUBLE
Request type:     DBR_DOUBLE
Element count:    1

Here we see that the PV “LN-TS{EVR:1A-SFP}Pwr:RX-I” is served from port number 5064 of

$ cainfo LN-RF{AMP:1}Amp-Sts
State:            connected
Host:             linacioc01.cs.nsls2.local:36349
Access:           read, write
Native data type: DBF_ENUM
Request type:     DBR_ENUM
Element count:    1

Here is another example where the hostname is shown instead of an IP address. Also this server has more than one IOC, and the one in question is using port 36349.

Find which process is using a TCP port (Linux only)

Super-user (root) permission is required to find which Linux process is bound to a particular TCP port.

To continue the example from above. On the server linacioc01.cs.nsls2.local we run:

$ sudo netstat -tlpn | grep 36349
tcp        0      0 *               LISTEN      4627/s7ioc

This tells us that TCP port 36349 is bound by process ID (PID) 4627, which has the process name of ‘s7ioc’.

Find information about a process (Linux only)

The ps command can give some information, including the command used to start the process. This often contains enough information to identify where the IOC’s files can be found.

$ ps aux|grep 4627
softioc   4627  1.5  0.0  93748  6616 pts/23   Ssl+ Jan07 744:18 ../../bin/linux-x86/s7ioc /epics/iocs/RF-CONTROL/iocBoot/iocrf-control/st.cmd

There are several pieces of information available under /proc which are useful. The entry /proc/<pid>/cwd is a symbolic link to the current working directory of the process. There is also /proc/<pid>/exe which links to the executable.

$ sudo ls -l /proc/4627/cwd
lrwxrwxrwx 1 softioc softioc 0 Feb 10 11:49 /proc/4627/cwd -> /epics/iocs/RF-CONTROL
$ sudo ls -l /proc/4627/exe
lrwxrwxrwx 1 softioc softioc 0 Jan  7 09:58 /proc/4627/exe -> /epics/iocs/RF-CONTROL/bin/linux-x86/s7ioc

Additional: Finding the procServ/screen running an IOC (Linux only)

The ps command can also tell us the PID of the parent of the IOC process. The techniques of step 3 can also be applied to the parent.

$ ps -eo pid,ppid,user,cmd|grep 4627
4627  4566 softioc  ../../bin/linux-x86/s7ioc /epics/iocs/RF-CONTROL/iocBoot/iocrf-control/st.cmd

The parent PID in the second column is 4566.

$ ps aux|grep 4566
softioc   4566  0.0  0.0   3452   592 ?        Ss   Jan07   2:18 /usr/bin/procServ -q -c /epics/iocs/RF-CONTROL/iocBoot/iocrf-control -i ^D^C^] -p /var/run/ -n RF-CONTROL --restrict --logfile=/var/log/softioc-RF-CONTROL.log 4057 /epics/iocs/RF-CONTROL/iocBoot/iocrf-control/st.cmd

And to complete the circle, and get access to the IOC console, we find which TCP port this procServ instance is bound to.

$ sudo netstat -tlpn|grep 4566
tcp        0      0*               LISTEN      4566/procServ
$ telnet localhost 4057
epics> dbpr LN-RF{AMP:1}Amp-Sts
ASG:                DESC: Ampl.500 MHz E-Source             DISA: 0
DISP: 0             DISV: 1             NAME: LN-RF{AMP:1}Amp-Sts
RVAL: 16            SEVR: NO_ALARM      STAT: NO_ALARM      SVAL: 0
TPRO: 0             VAL: 1