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.
632 questions
4
votes
0
answers
225
views
Confused about SIGINT trap
I am confused about the processing of SIGINT and EXIT traps in Bash scripts.
I wrote this script to test:
#!/usr/bin/env bash
set -e
exit_trap() {
printf "In exit_trap \$?=$?\n"
exit 0
...
- 2,380
0
votes
0
answers
30
views
Signal handling in debugger in linux
I am working on a debugger and found an issue.
I start at the beginning of the dynamic linker (this is a low-level debugger). At this address, I set it so that for a particular signal, the process ...
4
votes
1
answer
237
views
Why SIGTSTP (^Z/Ctrl-Z/suspend) doesn't work when process blocked redirecting write into a FIFO/pipe not open for reading yet? And what to do then?
Sometimes, a command is stalled attempting to write to a FIFO/pipe that no other process is currently reading from, but typing Ctrl-Z to put the process to the background by sending it the SIGTSTP ...
- 454
1
vote
2
answers
55
views
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
2
votes
1
answer
89
views
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 ...
- 8,897
3
votes
2
answers
172
views
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
2
votes
1
answer
288
views
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
2
votes
1
answer
78
views
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
1
vote
2
answers
139
views
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
0
votes
1
answer
147
views
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
0
votes
0
answers
58
views
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
1
vote
1
answer
84
views
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 ...
- 651
1
vote
2
answers
91
views
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 ...
- 651
1
vote
1
answer
86
views
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}"...
- 1,704
1
vote
1
answer
145
views
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:
() ...
- 613