Questions tagged [signals]
A signal is a message which can be sent to a running process. Signals can be initiated by programs, users, or administrators.
630 questions
1vote
2answers
33views
Why a signal that is blocked not shown up in SigPnd of /proc/pid/status when it is sent
Fact A signal may be blocked, which means that it will not be delivered until it is later unblocked. Between the time when it is generated and when it is delivered a signal is said to be pending. ...
- 715
2votes
1answer
62views
Detectng missed SIGWINCH in Bash extension, when apparent terminal size has not changed
I maintain an extension for the Bash environment called Basta. Basta provides a scroll-protected status line at the bottom of your ANSI/VT100 terminal. When Basta sets itself up, the effective number ...
- 8,827
3votes
2answers
112views
Why does the linux manual say nothing about generating a SIGCHLD signal when the child resumes execution?
I am using linux (ubuntu). When I type man 7 signal (manual 2020-12-21) in my terminal, I find the following for the SIGCHLD: SIGCHLD P1990 Ign Child stopped or terminated So, it states ...
- 517
2votes
1answer
193views
Why does the SIGCHLD generated by process continuation not activate the trap?
I am using linux (Ubuntu) and bash. I made a simple Go program. Literally infinite for-loop that prints text every 20 seconds. package main import ( "fmt" "time" ) func ...
- 517
2votes
1answer
58views
Why does the termination of the parent terminate the child when it is in the suspend (T) state?
I am using Ubuntu (linux). I have the following two simple programs. Parent: package main import ( "fmt" "syscall" "time" ) func main() { attr := &...
- 517
1vote
2answers
91views
Why does the kill command not work for SIGTSTP, but works for some other signals (SIGSTOP/SIGINT etc.)?
I have the following two simple programs. Parent: package main import ( "fmt" "syscall" ) func main() { attr := &syscall.ProcAttr{ Files: []uintptr{0, 1, ...
- 517
0votes
1answer
86views
Why does a SIGTSTP signal not handled by the parent move the entire group to the background (contrary to written in TTY demystified)?
I started learning about linux tty(s) and signals and ran into some trouble. I am reading and using The TTY demystified as a reference. I made two simple golang programs. Parent: package main import (...
- 517
0votes
0answers
43views
Why does sudo change process session id using setsid()?
I've been writing a script that spawns a child process as a different user via sudo then I realized that my script is not getting SIGINT as opposed to when I run it without sudo. As suspected strace ...
- 101
1vote
1answer
57views
Hit a strange signal settings of a kernel thread in Linux
I am working on an embedded Linux system (kernel-5.10.24), and using busybox as init. Now I hit a strange problem about signal settings of a kernel thread in system. The kernel thread is from a device ...
- 591
1vote
2answers
53views
Failed to core dump with send_sig(task, SIGSEGV, 1) from Linux kernel
I am working in an embedded Linux system, and now I want to trigger a core dump from within kernel by using send_sig(task, SIGSEGV, 1). There is a process A having 10 threads, occasionally, there is a ...
- 591
1vote
1answer
43views
Prevent SIGINT propagation from subshell to parent shell in Zsh
I need to prevent SIGINT (Ctrl-C) from propagating from a subshell to its parent shell functions in Zsh. Here's a minimal example: function sox-record { local output="${1:-$(mktemp).wav}"...
- 1,684
1vote
1answer
106views
Is there a race condition in bash when terminating a script with a subprocess with a signal?
#!/bin/bash ( sleep 10; echo foo; ) echo bar start to run the code during the sleep, send SIGINT (Ctrl+C) is there a chance of ever seeing "bar" on the output? The reasoning being: () ...
- 583
13votes
3answers
934views
Inconsistent “unzip -l … | grep -q …” results with pipefail
The following Bash function gave inconsistent results: # $1 Path to ZIP archive. # Exits with 0 status iff it contains a “.mp3” or “.flac” file. mp3_or_flac_in_zip() { local archive=${1:?No ...
- 389
1vote
1answer
135views
A few potential race conditions with signals and PIDs
I'm aware that because of PID-reuse on Unix-like kernels, signals can be delivered to the wrong process if they are sent after the PID has already been reaped. Discussion of what follows will probably ...
- 113
0votes
0answers
28views
EINTR implementation in the kernel sources - statfs & newfstatat
I'm trying to locate where in the kernel source files does statfs and newfstatat syscalls might fail with EINTR (due to a pending signal). The man pages list EINTR as one of the possible errors these ...
- 101
