Quite useful when one has got multiple jails running their own crons.
Obtained from FreeBSD.
--
Michal Belczyk
Index: cron/cron.8
===================================================================
RCS file: /home/dcvs/src/usr.sbin/cron/cron/cron.8,v
retrieving revision 1.2
diff -u -r1.2 cron.8
--- cron/cron.8 17 Jun 2003 04:29:53 -0000 1.2
+++ cron/cron.8 14 Mar 2006 21:57:28 -0000
@@ -26,6 +26,8 @@
.Nd daemon to execute scheduled commands (Vixie Cron)
.Sh SYNOPSIS
.Nm
+.Op Fl j Ar jitter
+.Op Fl J Ar rootjitter
.Op Fl s
.Op Fl o
.Op Fl x Ar debugflag Ns Op , Ns Ar ...
@@ -79,6 +81,27 @@
.Pp
Available options:
.Bl -tag -width indent
+.It Fl j Ar jitter
+Enable time jitter.
+Prior to executing commands,
+.Nm
+will sleep a random number of seconds in the range from 0 to
+.Ar jitter .
+This won't affect superuser jobs (see
+.Fl J ) .
+A value for
+.Ar jitter
+must be between 0 and 60 inclusive.
+Default is 0, which effectively disables time jitter.
+.Pp
+This option can help to smooth down system load spikes during
+moments when a lot of jobs are likely to start at once, e.g.,
+at the beginning of the first minute of each hour.
+.It Fl J Ar rootjitter
+Enable time jitter for superuser jobs.
+The same as
+.Fl j
+except that it will affect jobs run by the superuser only.
.It Fl s
Enable special handling of situations when the GMT offset of the local
timezone changes, such as the switches between the standard time and
Index: cron/cron.c
===================================================================
RCS file: /home/dcvs/src/usr.sbin/cron/cron/cron.c,v
retrieving revision 1.6
diff -u -r1.6 cron.c
--- cron/cron.c 18 Dec 2004 22:48:03 -0000 1.6
+++ cron/cron.c 14 Mar 2006 20:59:06 -0000
@@ -50,8 +50,8 @@
{
char **dflags;
- fprintf(stderr, "usage: cron [-s] [-o] [-x debugflag[,...]]\n");
- fprintf(stderr, "\ndebugflags: ");
+ fprintf(stderr, "usage: cron [-j jitter] [-J rootjitter] "
+ "[-s] [-o] [-x debugflag[,...]]\n");
for(dflags = DebugFlagNames; *dflags; dflags++) {
fprintf(stderr, "%s ", *dflags);
@@ -409,9 +409,22 @@
parse_args(int argc, char **argv)
{
int argch;
+ char *endp;
- while ((argch = getopt(argc, argv, "osx:")) != -1) {
+ while ((argch = getopt(argc, argv, "j:J:osx:")) != -1) {
switch (argch) {
+ case 'j':
+ Jitter = strtoul(optarg, &endp, 10);
+ if (*optarg == '\0' || *endp != '\0' || Jitter > 60)
+ errx(ERROR_EXIT,
+ "bad value for jitter: %s", optarg);
+ break;
+ case 'J':
+ RootJitter = strtoul(optarg, &endp, 10);
+ if (*optarg == '\0' || *endp != '\0' || RootJitter > 60)
+ errx(ERROR_EXIT,
+ "bad value for root jitter: %s", optarg);
+ break;
case 'o':
dst_enabled = 0;
break;
Index: cron/cron.h
===================================================================
RCS file: /home/dcvs/src/usr.sbin/cron/cron/cron.h,v
retrieving revision 1.4
diff -u -r1.4 cron.h
--- cron/cron.h 10 Mar 2004 18:27:26 -0000 1.4
+++ cron/cron.h 14 Mar 2006 20:08:44 -0000
@@ -269,6 +269,8 @@
char *ProgramName;
int LineNumber;
+unsigned Jitter,
+ RootJitter;
time_t TargetTime;
# if DEBUGGING
@@ -284,6 +286,8 @@
*DowNames[],
*ProgramName;
extern int LineNumber;
+extern unsigned Jitter,
+ RootJitter;
extern time_t TargetTime;
# if DEBUGGING
extern int DebugFlags;
Index: cron/do_command.c
===================================================================
RCS file: /home/dcvs/src/usr.sbin/cron/cron/do_command.c,v
retrieving revision 1.6
diff -u -r1.6 do_command.c
--- cron/do_command.c 18 Dec 2004 22:48:03 -0000 1.6
+++ cron/do_command.c 14 Mar 2006 20:09:36 -0000
@@ -159,6 +159,13 @@
Debug(DPROC, ("[%d] grandchild process Vfork()'ed\n",
getpid()))
+ if (e->uid == ROOT_UID)
+ Jitter = RootJitter;
+ if (Jitter != 0) {
+ srandom(getpid());
+ sleep(random() % Jitter);
+ }
+
/* write a log message. we've waited this long to do it
* because it was not until now that we knew the PID that
* the actual user command shell was going to get and the
