Sentinel mode: restart the program on certain conditions

* Makefile.am: Create the ChangeLog file from git log.
* configure.ac: Request git2chg
* src/com_start.c: Use sigaction instead of signal.
* src/genrc.8: Document new options.
* src/genrc.c: New options --restart-on-exit and --restart-on-signal.
* src/genrc.h (str_to_sig, str_to_int): New prototypes.
(add_restart_condition): New prototype.
* src/sentinel.c (restart_on, add_restart_condition):
(check_failure_rate): New functions.
(wait_loop): Return if restart is requested.
(sentinel): Restart the program if needed.

1 files changed, 56 insertions, 2 deletions

diff --git a/src/genrc.8 b/src/genrc.8
index 00522ee..959a00e 100644
--- a/src/genrc.8
+++ b/src/genrc.8
@@ -10,13 +10,13 @@
 .\" but WITHOUT ANY WARRANTY; without even the implied warranty of
 .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 .\" GNU General Public License for more details.
 .\"
 .\" You should have received a copy of the GNU General Public License
 .\" along with genrc.  If not, see <http://www.gnu.org/licenses/>. 
-.TH GENRC 8 "May 17, 2018" "GENRC" "Genrc User Manual"
+.TH GENRC 8 "May 20, 2018" "GENRC" "Genrc User Manual"
 .SH NAME
 genrc \- generic system initialization script helper
 .SH SYNOPSIS
 .nh
 .na
 \fBgenrc\fR\
@@ -33,12 +33,14 @@ genrc \- generic system initialization script helper
  [\fB\-\-group=\fIGROUP\fR[,\fIGROUP\fR...]]\
  [\fB\-\-help\fR]\
  [\fB\-\-no\-reload\fR]\
  [\fB\-\-pid\-from=\fISOURCE\fR]\
  [\fB\-\-pidfile=\fIPIDFILE\fR]\
  [\fB\-\-program=\fIPROGRAM\fR]\
+ [\fB\-\-restart\-on\-exit=\fR[\fB!\fR]\fISTATUS\fR[\fB,\fISTATUS\fR...]]\
+ [\fB\-\-restart\-on\-signal=\fR[\fB!\fR]\fISIG\fR[\fB,\fISIG\fR...]]\
  [\fB\-\-sentinel\fR]\
  [\fB\-\-signal\-reload=\fISIG\fR]\
  [\fB\-\-signal\-stop=\fISIG\fR]\
  [\fB\-\-timeout=\fISECONDS\fR]\
  [\fB\-\-user=\fIUSER\fR]\
  [\fB\-\-usage\fR]\
@@ -98,12 +100,36 @@ with the priority \fBinfo\fR and the error with the priority
 .PP
 If the \fB\-\-create\-pidfile=\fIFILENAME\fR option is given together with
 \fB\-\-sentinel\fR, the PID of the subsidiary command will be stored
 in \fIFILE\fR. The file will be unlinked after the subsidiary command
 terminates. Unless the \fB\-\-pid\-from\fR option is given,
 \fB\-\-pid\-from=FILE:\fIFILENAME\fR will be assumed.
+.PP
+In sentinel mode, it is possible to restart the program if it
+terminates with a specific exit code or on a specific signal. This is
+controlled by the \fB\-\-restart\-on\-exit\fR and 
+\fB\-\-restart\-on\-signal\fR options. Use this feature to ensure the
+service provided by the program won't get terminated because of
+hitting a bug or encountering an unforeseen external condition. For
+example, the following two options will ensure that the program will
+be terminated only if it exits with status 0 or it is terminated by
+SIGTERM or SIGQUIT signal:
+.EX
+--restart-on-exit='!0' --restart-on-signal='!TERM,QUIT'
+.EE
+.PP
+If restarts are requested, \fBgenrc\fR will control how often it has
+to restart the program using the same algorithm as
+.B init (8).
+Namely, if the program is restarted more than 10 times within two
+minutes, \fBgenrc\fR will disable subsequent restarts for the next
+5 minutes. If the \fB\-\-create\-pidfile\fR option was used, the
+PID of the controlling \fBgenrc\fR process will be stored in the
+file during that interval. If the \fBSIGHUP\fR signal is delivered
+during the sleep interval, the sleep will be broken prematurely and
+the program restarted again.
 .SS status
 In \fBstatus\fR mode \fBgenrc\fR verifies if the \fICOMMAND\fR is
 already running and outputs its status on the standard output. To this
 effect, it uses an abstraction called \fIPID source\fR, which allows
 it to determine the PID of the program by its name of command line.
 .PP
@@ -185,15 +211,43 @@ Makes \fBreload\fR equivalent to \fBrestart\fR.
 \fB\-p\fR, \fB\-\-program=\fIPROGRAM\fR
 Name of the program to run.
 .TP
 \fB\-P\fR, \fB\-\-pid\-from=\fISOURCE\fR
 Where to look for PIDs of the running programs.
 .TP
+\fB\-\-restart\-on\-exit=\fR[\fB!\fR]\fISTATUS\fR[\fB,\fISTATUS\fR...]
+This option takes effect when used together with
+\fB\-\-sentinel\fR. If the program terminates with one of status
+codes listed as the argument to this option, it will be immediately
+restarted. The exclamation mark at the start of the list inverts the
+set, e.g. \fB\-\-restart\-on\-exit='!0,1'\fR means restart unless the
+program exit code is 0 or 1. Note the use of quotation to prevent the
+\fB!\fR from being interpreted by the shell.
+.TP
+\fB\-\-restart\-on\-signal=\fR[\fB!\fR]\fISIG\fR[\fB,\fISIG\fR...]
+This option takes effect when used together with
+\fB\-\-sentinel\fR. If the program terminates due to receiving one of
+the signals from this list, it will be immediately restarted. Each
+\fISIG\fR is either a signal number, or a signal name, as listed in
+.BR signal (7).
+The \fBSIG\fR prefix can be omitted from the signal name. Names are
+case-insensitive. Thus, \fB1\fR, \fBHUP\fR, \fBSIGHUP\fR, and
+\fBsighup\fR all stand for the same signal.
+.sp
+The exclamation mark at the start of the list complements the signal
+set, so that e.g. \fB\-\-restart\-on\-signal='!TERM,QUIT,INT'\fR will
+restart the program unless it terminates on one of the listed signals.
+.TP
 \fB\-\-sentinel\fR
 \fIPROGRAM\fR runs in foreground; disconnect from the controlling
-terminal, run it and act as a sentinel.
+terminal, start it and run in background until it terminates. The
+program's stdout and stderr are sent to the syslog facility
+\fBdaemon\fR, priorities \fBinfo\fR and \fBerr\fR, correspondingly.
+
+See the options \fB\-\-restart\-on\-exit\fR and
+\fB\-\-restart\-on\-signal\fR for details on how to restart the program.
 .TP
 \fB\-\-signal\-reload=\fISIG\fR
 Signal to send on reload (default: \fBSIGHUP\fR). Setting it to 0 is
 equivalent to \fB\-\-no\-reload\fR.
 .TP
 \fB\-\-signal\-stop=\fISIG\fR