fix machinectl shell (in machined) (#7785)

4c253ed broke machined
$machinectl shell arch
Failed to get shell PTY: Input/output error

Closes: #7779

v2: do not drop DEATHSIG flag

1 files changed, 5 insertions, 1 deletions

diff --git a/src/basic/process-util.c b/src/basic/process-util.c
index cb92bab0f..940302e6f 100644
--- a/src/basic/process-util.c
+++ b/src/basic/process-util.c
@@ -1251,10 +1251,14 @@ int safe_fork_full(
         }
 
         if (flags & FORK_DEATHSIG) {
+                pid_t ppid;
                 /* Let's see if the parent PID is still the one we started from? If not, then the parent
                  * already died by the time we set PR_SET_PDEATHSIG, hence let's emulate the effect */
 
-                if (getppid() != original_pid) {
+                ppid = getppid();
+                if (ppid == 0)
+                        /* Parent is in a differn't PID namespace. */;
+                else if (ppid != original_pid) {
                         log_debug("Parent died early, raising SIGTERM.");
                         (void) raise(SIGTERM);
                         _exit(EXIT_FAILURE);