Configuration Information:
Machine: x86_64
OS: linux-gnu (Debian 13, WSL2 kernel 6.18)
Bash Version: 5.2.37(1)-release (Debian package); also 5.3.20(1)-release, built
from bash-5.3.tar.gz plus patches 001-020 with a plain ./configure
Description:
With a trap on SIGTERM, a loop whose body runs `continue` sometimes never
runs the trap: the signal is lost and the script keeps running. Sending
SIGTERM to 40 copies of the script below, 1 second after they start, left
9-17 of the 40 running after 3 seconds, on both versions, on an idle
machine. The trap's first command (an append to a file) did not run in
those copies, so the trap was never entered, not entered and then failing.
The same loop with `:` in place of `continue` lost none in 80 tries; a
`while read` loop whose body only runs `continue` lost 10 of 80.
Repeat-By:
cat >forcont.sh <<'EOF'
trap 'echo "$$" >>trapped; exit 143' TERM
while :; do for ((i = 0; i < 20000; i++)); do continue; done; done
EOF
pids=()
for i in $(seq 1 40); do bash forcont.sh & pids+=($!); done
sleep 1; kill -TERM "${pids[@]}"; sleep 3
alive=0
for p in "${pids[@]}"; do kill -0 "$p" 2>/dev/null && alive=$((alive +
1)); done
echo "alive=$alive of 40" # expected 0; we see 9-17
kill -KILL "${pids[@]}" 2>/dev/null
Fix:
Unknown. As a workaround we run the loop in a child process and have
the parent, which only waits, receive the signal.
Cheers.
[cid:6cc5eeca-6aac-4e58-9c0f-4ad1acf0ce02]<https://www.skillonnet.com/>
Dimitrios Christou
DevOps
Email: [email protected]
SkillOnOps
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