journald: introduce new "systemd-journal" group and make it own the journal files

Previously all journal files were owned by "adm". In order to allow
specific users to read the journal files without granting it access to
the full "adm" powers, introduce a new specific group for this.

"systemd-journal" has to be created by the packaging scripts manually at
installation time. It's a good idea to assign a static UID/GID to this
group, since /var/log/journal might be shared across machines via NFS.

This commit also grants read access to the journal files by default to
members of the "wheel" and "adm" groups via file system ACLs, since
these "almost-root" groups should be able to see what's going on on the
system. These ACLs are created by "make install". Packagers probably
need to duplicate this logic in their postinst scripts.

This also adds documentation how to grant access to the journal to
additional users or groups via fs ACLs.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/journal/journald-server.c b/src/journal/journald-server.c
index 654f7ace21..ac565c7ece 100644
--- a/src/journal/journald-server.c
+++ b/src/journal/journald-server.c
@@ -174,7 +174,7 @@ static uint64_t available_space(Server *s) {
 }
 
 static void server_read_file_gid(Server *s) {
-        const char *adm = "adm";
+        const char *g = "systemd-journal";
         int r;
 
         assert(s);
@@ -182,9 +182,9 @@ static void server_read_file_gid(Server *s) {
         if (s->file_gid_valid)
                 return;
 
-        r = get_group_creds(&adm, &s->file_gid);
+        r = get_group_creds(&g, &s->file_gid);
         if (r < 0)
-                log_warning("Failed to resolve 'adm' group: %s", strerror(-r));
+                log_warning("Failed to resolve '%s' group: %s", g, strerror(-r));
 
         /* if we couldn't read the gid, then it will be 0, but that's
          * fine and we shouldn't try to resolve the group again, so