getppid#

Return the process ID of the current process’s parent.

getppid is a thin wrapper over the POSIX getppid(2) system call. It takes no arguments and returns an integer — the PID of whatever process forked (or execed into) the running program. Combined with $$ (the current process’s own PID), it is the standard way for a child to identify the process that spawned it.

Synopsis#

my $parent = getppid;

What you get back#

A positive integer — the PID of the parent process. On Linux this is 1 (init / systemd) once the original parent has exited and the child has been reparented; there is no special “orphaned” return value, the reparenting is transparent. Never returns undef or 0 on a supported platform; the underlying syscall is specified to always succeed.

Global state it touches#

None. getppid reads the kernel’s process table for the current process; it does not touch any Perl special variable. Note that $$ holds this process’s PID, not the parent’s — fetch the parent with getppid explicitly.

Examples#

Identify the parent that launched this script:

printf "my pid is %d, my parent is %d\n", $$, getppid;

Detect orphaning — a common idiom for daemons that want to exit when their controlling process goes away:

while (1) {
    last if getppid == 1;       # parent died, we've been reparented to init
    do_work();
    sleep 1;
}

Child process reports back to its parent after fork:

my $pid = fork // die "fork failed: $!";
if ($pid == 0) {
    warn "child $$ spawned by $>, parent is " . getppid . "\n";
    exit 0;
}
waitpid $pid, 0;

Compare before and after fork to confirm the relationship:

my $before = $$;
my $pid = fork // die $!;
if ($pid == 0) {
    die "parent mismatch" unless getppid == $before;
    exit;
}
waitpid $pid, 0;

Edge cases#

No arguments, no parentheses needed: getppid is a niladic built-in. Write getppid or getppid(); both parse identically. Do not try to pass a PID argument — unlike getpgrp, there is no “parent of another process” form.
Orphan reparenting is invisible: if the original parent exits, the kernel reparents the process (to init/systemd on Linux, or to the nearest ancestor with PR_SET_CHILD_SUBREAPER set). getppid silently starts returning the new parent’s PID. Code that caches the return value at startup and compares later is the standard way to detect this.
Race at startup: calling getppid extremely early, before the kernel has finished setting up the process, is not a concern in user Perl code — by the time the interpreter is running, the parent PID is stable.
PID wraparound: PIDs are recycled. A stored parent PID can, over long-running time, refer to a different process than the original parent even without reparenting. Use getppid == 1 (or the equivalent subreaper PID), not equality against a saved value, when the intent is “has my parent died?”.
Threads: since Perl 5.16 the Linux LinuxThreads workaround has been removed. getppid now always returns what the kernel reports for the current thread group.

Differences from upstream#

Fully compatible with upstream Perl 5.42.