Re: Return codes for archive and restore commands

On Wed, Nov 28, 2018 at 11:00:31AM +0000, PG Doc comments form wrote:
> For the archive command:
> <=128 There are not errors in the PostgreSQL log (messages with severity
> equal or higher than ERROR). Firstly 3 messages of type LOG about fault,
> then WARNING about this and pause for 1 minute, then repeated.
> >=129 FATAL error in the PostgeSQL log. The message about stoping an archive
> process, but not the database. Repeated after roughly 16 seconds.

This code is around for some time, and comes from this commit:
commit: 3ad0728c817bf8abd2c76bd11d856967509b307c
author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
date: Tue, 21 Nov 2006 20:59:53 +0000
committer: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
date: Tue, 21 Nov 2006 20:59:53 +0000
On systems that have setsid(2) (which should be just about everything except
Windows), arrange for each postmaster child process to be its own process
group leader, and deliver signals SIGINT, SIGTERM, SIGQUIT to the whole
process group not only the direct child process. This provides saner behavior
for archive and recovery scripts; in particular, it's possible to shut down a
warm-standby recovery server using "pg_ctl stop -m immediate", since delivery
of SIGQUIT to the startup subprocess will result in killing the waiting
recovery_command. Also, this makes Query Cancel and statement_timeout apply
to scripts being run from backends via system(). (There is no support in the
core backend for that, but it's widely done using untrusted PLs.) Per gripe
from Stephen Harris and subsequent discussion.

The relevant part if pgarch_archiveXlog() in pgarch.c, and this part
is most relevant:
* Per the Single Unix Spec, shells report exit status > 128 when a
* called command died on a signal.

> In this case PostgreSQL tries confirm rules for return codes of a unix
> shell. A unix shell return 126 in the case of "command not executable", 127
> in the case "command not found", 128+# of signal in the case if application
> interrupted by uncatched signal.

If you were to rewrite those paragraphs or make them more precise, how
would you actually shape your suggestions? I personally quite like the
current formulations, but I am rather used to it to be honest.
--
Michael