Is there a reason GNU/Linux lacks SIGINFO?

svenper · 2015-10-30 10:46:19

I know that GNU’s Not Unix, but this feature would make a lot of sense. It’s just another signal on BSD, that can also easily be sent to the current running process by the hotkey ^T. It’s logically more appealing as it describes what interaction the user wants with a process. Want to view the progress of dd or cp? SIGUSR1? Too confusing. SIGINFO? Bingo! That’s exactly what I wanted to do.

There is some code in glibc that mentions SIGINFO, but only in relation to BSD or HURD.

So why isn’t it in GNU/Linux? Is there a compatibility issue? Is it because it’s not in POSIX? Is it ‘bloat’? Did they just forget about it?

Last edited by svenper (2015-10-30 10:47:11)

mauritiusdadd · 2015-10-30 11:07:56

For what I know GNU/Linux includes a SIGINFO signal, but it is equivalent to SIGPWR

$ man 7 signal
  ...
       Signal       Value     Action   Comment
       ────────────────────────────────────────────────────────────────────
       SIGIOT         6        Core    IOT trap. A synonym for SIGABRT
       SIGEMT       7,-,7      Term
       SIGSTKFLT    -,16,-     Term    Stack fault on coprocessor (unused)
       SIGIO       23,29,22    Term    I/O now possible (4.2BSD)
       SIGCLD       -,-,18     Ign     A synonym for SIGCHLD
       SIGPWR      29,30,19    Term    Power failure (System V)
       SIGINFO      29,-,-             A synonym for SIGPWR
       SIGLOST      -,-,-      Term    File lock lost (unused)
       SIGWINCH    28,28,20    Ign     Window resize signal (4.3BSD, Sun)
       SIGUNUSED    -,31,-     Core    Synonymous with SIGSYS

       (Signal 29 is SIGINFO / SIGPWR on an alpha but SIGLOST on a sparc.)
  ...

-- edit: I think that since they are not defined in the POSIX standard, each system implements them in their on way.

Last edited by mauritiusdadd (2015-10-30 11:10:13)

svenper · 2015-10-30 15:35:39

Well, that’s odd. On my Arch basic setup PWR just kills the process and INFO doen’t exist. Try for youself:

dd if=/dev/zero of=/dev/null

in other terminal:

killall -PWR dd

(re-run first command in first terminal)

killall -INFO dd

PWR gives a power fail error and INFO is an “unknown signal”.

to list available signals:

killall -l

and INFO isn’t in the list.

Is this a bug or a feature?

mauritiusdadd · 2015-10-30 16:14:45

svenper wrote:

Well, that’s odd. On my Arch basic setup PWR just kills the process and INFO doen’t exist.

.
Well, it seems that the man pages are slightly outdated since it seems that the SIGINFO signal is actually not defined in the linux version of the GNU C library. However, note that it is SIGINFO that is a synonym to SIGPWR and not the other way around.

--edit: actuall re-reading the man page

man 7 signal wrote:

Linux supports the standard signals listed below. Several signal numbers are architecture-dependent, as indicated in the "Value" column. (Where three values are given, the first one is usually valid for alpha and sparc, the middle one for x86, arm, and most other architectures, and the last one for mips. (Values for parisc are not shown; see the Linux kernel source for signal numbering on that architecture.) A - denotes that a signal is absent on the corresponding architecture.)

So it seems that the signal SIGINFO is only available for the alpha and sparc architectures.

Last edited by mauritiusdadd (2015-10-30 16:22:18)

svenper · 2015-10-30 18:14:19

mauritiusdadd wrote:

So it seems that the signal SIGINFO is only available for the alpha and sparc architectures.

Ok, that explains things, but it’s still very odd that SIGINFO exists on x86 BSD, but not x86 GNU/Linux.

Alad · 2015-10-30 19:33:09

http://lkml.iu.edu/hypermail/linux/kern … 03374.html

Arch Linux

#1 2015-10-30 10:46:19

Is there a reason GNU/Linux lacks SIGINFO?

#2 2015-10-30 11:07:56

Re: Is there a reason GNU/Linux lacks SIGINFO?

#3 2015-10-30 15:35:39

Re: Is there a reason GNU/Linux lacks SIGINFO?

#4 2015-10-30 16:14:45

Re: Is there a reason GNU/Linux lacks SIGINFO?

#5 2015-10-30 18:14:19

Re: Is there a reason GNU/Linux lacks SIGINFO?

#6 2015-10-30 19:33:09

Re: Is there a reason GNU/Linux lacks SIGINFO?

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