Add sysusers.d configuration file for systemd service

CMakeLists.txt

@@ -91,6 +91,11 @@ set(SYSTEMD_UNITDIR
     "${DETECTED_SYSTEMD_UNITDIR}"
     CACHE PATH "Install destination for the systemd postsrsd.service unit"
 )
+find_systemd_sysusers_destination(DETECTED_SYSTEMD_SYSUSERSDIR)
+set(SYSTEMD_SYSUSERSDIR
+    "${DETECTED_SYSTEMD_SYSUSERSDIR}"
+    CACHE PATH "Install destination for the sysusers.d configuration"
+)
 
 if(POSTSRSD_CHROOTDIR)
     file(RELATIVE_PATH CHROOTABLE_DATADIR "${POSTSRSD_CHROOTDIR}"
@@ -350,6 +355,10 @@ configure_file(
     "${CMAKE_CURRENT_SOURCE_DIR}/data/postsrsd.service.in"
     "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.service" @ONLY
 )
+configure_file(
+    "${CMAKE_CURRENT_SOURCE_DIR}/data/sysusers.conf.in"
+    "${CMAKE_CURRENT_BINARY_DIR}/sysusers.d/${PROJECT_NAME}.conf" @ONLY
+)
 
 install(TARGETS postsrsd RUNTIME DESTINATION ${CMAKE_INSTALL_SBINDIR})
 install(FILES "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.conf"
@@ -359,6 +368,9 @@ if(INSTALL_SYSTEMD_SERVICE)
     install(FILES "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.service"
             DESTINATION "${SYSTEMD_UNITDIR}"
     )
+    install(FILES "${CMAKE_CURRENT_BINARY_DIR}/sysusers.d/${PROJECT_NAME}.conf"
+            DESTINATION "${SYSTEMD_SYSUSERSDIR}"
+    )
 endif()
 
 if(GENERATE_SRS_SECRET)

cmake/utils.cmake

@@ -79,3 +79,26 @@ function(find_systemd_unit_destination var)
         )
     endif()
 endfunction()
+
+function(find_systemd_sysusers_destination var)
+    if(CMAKE_INSTALL_PREFIX MATCHES "^/usr/?$")
+        find_package(PkgConfig QUIET)
+        if(PkgConfig_FOUND)
+            pkg_get_variable(sysusersdir systemd sysusersdir)
+            set(${var}
+                "${sysusersdir}"
+                PARENT_SCOPE
+            )
+        else()
+            set(${var}
+                "/usr/lib/sysusers.d"
+                PARENT_SCOPE
+            )
+        endif()
+    else()
+        set(${var}
+            "/etc/sysusers.d"
+            PARENT_SCOPE
+        )
+    endif()
+endfunction()

data/sysusers.conf.in

@@ -0,0 +1 @@
+u @POSTSRSD_USER@ - "PostSRSd user" - -

doc/packaging.rst

@@ -60,13 +60,17 @@ users:
   installation secure by default, but less so for a distributed binary package.
 
 - ``INSTALL_SYSTEMD_SERVICE``: If set to ``ON`` (the default), a postsrsd.service
-  unit will be installed to start PostSRSd via systemd at boot time. You can disable
+  unit will be installed to allow starting PostSRSd via systemd. You can disable
   this if your distribution uses a different init system.
 
 - ``SYSTEMD_UNITDIR``: the intended install destination for the
   ``postsrsd.service`` file. The default should be fine for most systems, but
   you can override it if the auto-detected location is wrong.
 
+- ``SYSTEMD_SYSUSERSDIR``: the intended install destination for the
+  sysusers.d configuration file. The default should be fine for most systems, but
+  you can override it if the auto-detected location is wrong.
+
 - ``DEVELOPER_BUILD``: this makes the compiler treat all warnings as errors and
   enable as much of them as possible. While certainly useful for me as upstream
   developer (and for the Github CI), you should keep this option disabled. It