# EPICS

Where is EPICS Base (https://gitea.psi.ch/epics) installed?
```
echo $EPICS
```

Host architecture that EPICS Base runs on:
```
echo $EPICS_HOST_ARCH
```

Which channel access lib is being used in python?
```
[sls-vserv-bd-hla01-dev ~]$ which python
/bin/python
[sls-vserv-bd-hla01-dev playground]$ python3 -c "import ctypes; import epics.ca; print(epics.ca.find_libca())"
/usr/local/epics/base-7.0.9/lib/RHEL9-x86_64/libca.so
[sls-vserv-bd-hla01-dev ~]$ source /opt/gfa/python-3.10/latest/bin/activate
(base) [sls-vserv-bd-hla01-dev ~]$ which python
/opt/gfa/python-3.10/20220602/bin/python
(base) [sls-vserv-bd-hla01-dev ~]$  python3 -c "import ctypes; import epics.ca; print(epics.ca.find_libca())"
/opt/gfa/python-3.10/20220602/epics/lib/linux-x86_64/libca.so
```

How does the conda env configure which EPICS to use?

```
(base) [sls-vserv-bd-hla01-dev ~]$ cat /opt/gfa/python-3.10/20220602/etc/conda/activate.d/epics-base_activate.sh
export EPICS_BASE="/opt/gfa/python-3.10/20220602/epics"
export EPICS_HOST_ARCH="linux-x86_64"
export EPICS_BASE_HOST_BIN="/opt/gfa/python-3.10/20220602/epics/bin/linux-x86_64"
export EPICS_BASE_VERSION="7.0.5.0"
export PATH=$EPICS_BASE_HOST_BIN:$PATH
```

How does the conda env configure which EPICS python uses?
```
(base) [sls-vserv-bd-hla01-dev ~]$ cat /opt/gfa/python-3.10/20220602/etc/conda/activate.d/pyepics_activate.sh
export PYEPICS_LIBCA="${EPICS_BASE}/lib/${EPICS_HOST_ARCH}/libca.so"
```


Example reading from a PV:
```
[sls-vserv-bd-hla01-dev ~]$ /bin/python
Python 3.9.25 (main, Apr 17 2026, 00:00:00)
[GCC 11.5.0 20240719 (Red Hat 11.5.0-14)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from epics import PV
>>> pv = PV("AGEBD-PLAYGROUND-DEV:AO")
>>> pv.get()
5.0
>>>
```

## System python installed packages

```
/bin/python -m pip list -v
```

## Systemd Services

When ssh-ing into a machine, `/etc/profile.d/*` automatically gets sourced.

When running a `systemd` service, this does not happen.

That's why we need to source `/etc/profile.d/cas_12_epics.sh` in our startup script
to make sure that `EPICS` is configured properly.