How to make `xargs` ignore child's exit and keep processing further

Question

I sometimes run long xargs jobs overnight and it is really annoying to discover in the morning that xargs died somewhere in the middle, for example because of a segmentation fault in one single special case, as happened this night.

If even one xargs child is killed, it does not process any more input:

Console 1:

[09:35:48] % seq 40 | xargs -i --max-procs=4 bash -c 'sleep 10; date +"%H:%M:%S {}";'
xargs: bash: terminated by signal 15
09:35:58 3
09:35:58 4
09:35:58 2
<Exit with code 125>

Console 2:

[09:35:54] kill 5601

Can I somehow prevent xargs from stopping to process any more input once a child process dies and instead continue processing?

Answer 1

No, you can't. From the xargs sources at savannah.gnu.org:

if (WEXITSTATUS (status) == CHILD_EXIT_PLEASE_STOP_IMMEDIATELY)
  error (XARGS_EXIT_CLIENT_EXIT_255, 0,
         _("%s: exited with status 255; aborting"), bc_state.cmd_argv[0]);
if (WIFSTOPPED (status))
  error (XARGS_EXIT_CLIENT_FATAL_SIG, 0,
         _("%s: stopped by signal %d"), bc_state.cmd_argv[0], WSTOPSIG (status));
if (WIFSIGNALED (status))
  error (XARGS_EXIT_CLIENT_FATAL_SIG, 0,
         _("%s: terminated by signal %d"), bc_state.cmd_argv[0], WTERMSIG (status));
if (WEXITSTATUS (status) != 0)
  child_error = XARGS_EXIT_CLIENT_EXIT_NONZERO;

There's no flag around that check, or around the function that calls it. It does seem to be related to max procs, which I suppose makes sense: if you set max procs high enough, it won't bother checking until it's hit the limit, which you might get to be never.

A better solution for what you're trying to do might be to use GNU Make:

TARGETS=$(patsubst %,target-%,$(shell seq 1 40))

all: $(TARGETS)

target-%:
    sleep 10; date +"%H:%M:%S $*"

Then:

$ make -k -j4 

will have the same effect, and give you much better control.

Answer 2

Put another command in there to 'eat' the signal from the dying program.

I tried your example, initally as shown to prove the problem... 'killall sleep' kills the sleep process, interrupts bash, and xargs quits.

As a test, I stuck a 'run another command' type command in between xargs and bash... in this case '/usr/bin/time'. this time (no pun), killall sleep kills the sleep process, but the xargs continues on.

You would pipe time's output to /dev/null, and this would do exactly what you're looking for without a major rewrite of your existing process.

I imagine if I ponder for a moment I could come up with another program to do the same without the stderr chatter from '/usr/bin/time'. Or even write one myself, it's just a 'fork' (or exec() derivative).

Remember to use '/usr/bin/time', as I'm not sure the built-in 'time' from bash will do the same 'eating' of the signal.

Answer 3

Use trap:

$ seq 40 | xargs -i --max-procs=4 bash -c \
 'trap "echo erk; exit 1" INT TERM;  sleep 10; date +"%H:%M:%S {}";' fnord
16:07:39 2
16:07:39 4
erk
16:07:39 1
^C
erk
erk
erk
erk

Alternatively switch from shell to another language in which you can also set signal handlers.

Note also that after bash -c foo.. you should specify the value that $0 should take (here, fnord) so that the first word produced by seq doesn't get eaten.