Add respawn

Makefile

@@ -40,6 +40,7 @@ SRC = \
 	pidof.c             \
 	pivot_root.c        \
 	ps.c                \
+	respawn.c           \
 	rmmod.c             \
 	stat.c              \
 	su.c                \
@@ -67,6 +68,7 @@ MAN1 = \
 	pagesize.1          \
 	pidof.1             \
 	ps.1                \
+	respawn.1           \
 	stat.1              \
 	su.1                \
 	truncate.1          \

respawn.1

@@ -0,0 +1,12 @@
+.TH RESPAWN 1 ubase-VERSION
+.SH NAME
+\fBrespawn\fR - Spawn the given command repeatedly
+.SH SYNOPSIS
+\fBrespawn\fR [\fB-d\fI N\fR] \fIcmd\fR [\fIargs...\fR]
+.SH DESCRIPTION
+\fBrespawn\fR spawns the given \fIcmd\fR in a new session
+repeatedly.
+.SH OPTIONS
+.TP
+\fB-d\fR
+Set the delay between invocations of \fIcmd\fR.  It defaults to 0.

respawn.c

@@ -0,0 +1,54 @@
+/* See LICENSE file for copyright and license details. */
+#include <errno.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "util.h"
+
+static void
+usage(void)
+{
+	eprintf("usage: respawn [-d N] cmd [args...]\n");
+}
+
+int
+main(int argc, char **argv)
+{
+	pid_t pid;
+	int savederrno;
+	unsigned int delay = 0;
+
+	ARGBEGIN {
+	case 'd':
+		delay = estrtol(EARGF(usage()), 0);
+		break;
+	default:
+		usage();
+	} ARGEND;
+
+	if(argc < 1)
+		usage();
+
+	while (1) {
+		pid = fork();
+		if (pid < 0)
+			eprintf("fork:");
+		switch (pid) {
+		case 0:
+			if (setsid() < 0)
+				eprintf("setsid:");
+			execvp(argv[0], argv);
+			savederrno = errno;
+			weprintf("execvp %s:", argv[0]);
+			_exit(savederrno == ENOENT ? 127 : 126);
+			break;
+		default:
+			waitpid(pid, NULL, 0);
+			break;
+		}
+		sleep(delay);
+	}
+	/* not reachable */
+	return EXIT_SUCCESS;
+}