units: document why CAP_SYS_PTRACE is needed by journald

diff --git a/units/systemd-journald.service.in b/units/systemd-journald.service.in
index 1c43d8c863ab018ba5d934f5cde28a5ce94dfcff..eb4bd938d77d1d6cdf9a5e3276525e6150d37375 100644 (file)
--- a/units/systemd-journald.service.in
+++ b/units/systemd-journald.service.in
@@ -16,7 +16,6 @@ After=systemd-journald.socket systemd-journald-dev-log.socket systemd-journald-a
 Before=sysinit.target
 
 [Service]
-CapabilityBoundingSet=CAP_SYS_ADMIN CAP_DAC_OVERRIDE CAP_SYS_PTRACE CAP_SYSLOG CAP_AUDIT_CONTROL CAP_AUDIT_READ CAP_CHOWN CAP_DAC_READ_SEARCH CAP_FOWNER CAP_SETUID CAP_SETGID CAP_MAC_OVERRIDE
 DeviceAllow=char-* rw
 ExecStart=@rootlibexecdir@/systemd-journald
 FileDescriptorStoreMax=4224
@@ -42,6 +41,11 @@ SystemCallFilter=@system-service
 Type=notify
 @SERVICE_WATCHDOG@
 
+# In case you're wondering why CAP_SYS_PTRACE is needed, access to
+# /proc/<pid>/exec requires this capability. Thus if this cap is missing
+# _EXE/OBJECT_EXE fields will be missing from the journal entries.
+CapabilityBoundingSet=CAP_SYS_ADMIN CAP_DAC_OVERRIDE CAP_SYS_PTRACE CAP_SYSLOG CAP_AUDIT_CONTROL CAP_AUDIT_READ CAP_CHOWN CAP_DAC_READ_SEARCH CAP_FOWNER CAP_SETUID CAP_SETGID CAP_MAC_OVERRIDE
+
 # If there are many split up journal files we need a lot of fds to access them
 # all in parallel.
 LimitNOFILE=@HIGH_RLIMIT_NOFILE@