services: zabbix: Don't write user to configuration file.

The service already runs with the specified user and group, so there is no use
in writing it to the configuration files.  This change is mainly done for
compatibility with 'zabbix-agent2' which does not understand the User=
setting, but also to document the correct data type for the "group" setting.

* gnu/services/monitoring.scm (serialize-string): Filter USER and GROUP
fields.
(group?, serialize-group): Remove variables.
(zabbix-server-configuration, zabbix-agent-configuration): Document the GROUP
field as 'string'.
* doc/guix.texi (Monitoring Services): Adjust accordingly.

1 files changed, 6 insertions, 9 deletions

diff --git a/gnu/services/monitoring.scm b/gnu/services/monitoring.scm
index d6dc2c1e03..f12b7acb1f 100644
--- a/gnu/services/monitoring.scm
+++ b/gnu/services/monitoring.scm
@@ -224,15 +224,12 @@ Prometheus.")
 
 
 (define (serialize-string field-name val)
-  (if (and (string? val) (string=? val ""))
+  (if (or (eq? 'user field-name)
+          (eq? 'group field-name)
+          (and (string? val) (string=? val "")))
       ""
       (serialize-field field-name val)))
 
-(define group? string?)
-
-(define serialize-group
-  (const ""))
-
 (define include-files? list?)
 
 (define (serialize-include-files field-name val)
@@ -256,8 +253,8 @@ Prometheus.")
   (user
    (string "zabbix")
    "User who will run the Zabbix server.")
-  (group ;for zabbix-server-account procedure
-   (group "zabbix")
+  (group
+   (string "zabbix")
    "Group who will run the Zabbix server.")
   (db-host
    (string "127.0.0.1")
@@ -438,7 +435,7 @@ results in a Web interface.")))
    (string "zabbix")
    "User who will run the Zabbix agent.")
   (group
-   (group "zabbix")
+   (string "zabbix")
    "Group who will run the Zabbix agent.")
   (hostname
    (string "")