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2022-12-08T19:53:54Z

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Understanding the structure of a deployed EPICS IOC and environment, determining configuration, and parsing error messages.

== Linux-specific ==

=== Examine the environment with <code>env</code> ===

EPICS reads several "environment variables" during operation.
You can examine the current list of environment variables in a terminal (either bash or csh) using <code>env</code>.

To get the value of a particular environment variable, try
<code>env | grep VARIABLE</code> or <code>echo $VARIABLE </code>.

Particularly relevant ones are:

; PATH : list of folders which are searched for executable scripts and binaries. If you are seeing "command not found"-type errors, consider if $PATH is set correctly.
; EPICS_CA_ADDR_LIST : IP addresses that are contacted when searching for a CA (channel-access) variable. Important for any program which is accessing CA variables provided by a different program, possibly on a different host.
; EPICS_CA_AUTO_ADDR_LIST : (yes | no). Whether to also include the broadcast address for all configured network interfaces in the CA_ADDR_LIST. This automatically searches all computers on the same subnet for variables.
; EPICS_PVA_ADDR_LIST : As above, but for PVaccess variables.
; EPICS_PVA_AUTO_ADDR_LIST : As above, but for automatic use of broadcast addresses for PVaccess variables.

For example, when examining a GUI which should only connect to the channel access variables of a local instance of an IOC, you might expect to see a configuration like:

<pre>EPICS_CA_AUTO_ADDR_LIST=no
EPICS_CA_ADDR_LIST=127.0.0.255</pre>

=== Find library dependencies with ldd ===

Sometimes it is necessary to determine which versions of a shared library are linked into the IOC binary. On other occasions, an IOC binary will not run (typically, an immediate segfault) because a necessary linked library is missing.
<code>ldd</code> is a Linux tool which will list all linked dynamic (shared) libraries of a binary, to answer these questions. Execute <code>ldd -r</code> against the IOC '''binary''' (not startup script) and examine its output.

Example:

<pre>
$ cd ~/epics/synApps_6_2_1/ioc/IocSpinnaker/
$ ldd -r bin/rhel8-x86_64/SpinnakerApp
linux-vdso.so.1 (0x00007ffffb195000)
libADSpinnaker.so => /net/s100dserv/APSshare/epics/synApps_6_2_1/support/areaDetector-R3-12-1/ADSpinnaker/lib/rhel8-x86_64/libADSpinnaker.so (0x00007f149e6f9000)
libADGenICam.so => /net/s100dserv/APSshare/epics/synApps_6_2_1/support/areaDetector-R3-12-1/ADGenICam/lib/rhel8-x86_64/libADGenICam.so (0x00007f149e4e6000)
...
</pre>

The location of all found libraries will be listed in full, while any missing libraries will be noted:

<pre>
libfoo.so => not found
</pre>

=== View the full IOC output when running in screen ===

By default, IOCs built from the XXX template are controlled via a startup shell script:

<pre>ExampleIOC.sh (start|stop|status)</pre>

When you start an IOC this way, no output is immediately visible, and control returns to your terminal. It is possible to connect to the IOC console via

<pre>ExampleIOC.sh console</pre>

which opens a connection to <code>screen</code>, the Linux terminal multiplexer. Type <code>exit</code> at the IOC prompt to exit, or use <code>Ctrl-a Ctrl-d</code> (detach) to leave the IOC running in the background and return to the terminal. <code>Ctrl-a [</code> will change screen to scrollback-mode, where you will be able to examine the stored history of IOC output. Use <code>/</code> to search forward through the text, and <code>?</code> to search backwards, for example to find errors.

Troubleshooting EPICS IOCs - Revision history

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