Delay when CTRL + C -ing a Sudo command.

[Oglo12]

I am using sudo to run my package manager, but everytime I misstype a package name, I try to CTRL + C Sudo, and it takes around 7 seconds or so!

[millert]

Does this happen for all sudo commands or only certain ones? Can you give an exact example of a command that doesn't get interrupted properly?

[AlexBaranowski]

@Oglo12

Good package managers are written to handle signals. The CTRLC sends the SIGINT (number 2) signals. There are different signals - for context please read the man 7 signal or https://man.docs.euro-linux.com/EL%209/man-pages/signal.7.en.html

The signals that are supposed to "kill" or "stop" (called TERM type signals) process might be handled by a program (each program can define a set of signal handlers) except for some signals like SIGKILL (some signals are handled by the kernel).

So basically when you send the signal to the package manager like yum it does not stop at once as it has to ensure for example the following:

• package database is not corrupted
• any operations that are in progress do not damage the system
• the packages that are on the filesystem are in a proper state
• the locks are freed

And much much more. It's not trivial.

I also conducted simple tests:

#!/usr/bin/env bash

sudo yum clean all
sudo yum update -y &
YUM_UPDATE_PID=$(sudo pgrep yum)
echo "yum update pid: $YUM_UPDATE_PID"
sleep 1; 
sudo kill -2 $YUM_UPDATE_PID
wait

second test - without any sudo must be run as root.

#!/usr/bin/env bash

yum clean all
yum update -y &
YUM_UPDATE_PID=$(pgrep yum)
echo "yum update pid: $YUM_UPDATE_PID"
sleep 1; 
kill -2 $YUM_UPDATE_PID
wait

Both tests are run with time bash x.sh

Result with sudo:

[Alex@NormandySR2 ~]$ time bash x.sh 
0 files removed
yum update pid: 33213
Docker CE Stable - x86_64                                                                                                                                                            0.0  B/s |   0  B     00:05    
Error: Failed to download metadata for repo 'docker-ce-stable': Librepo was interrupted by a signal

real	0m5.648s
user	0m0.531s
sys	0m0.174s

Result without sudo:

[root@NormandySR2 ~]# time bash x.sh 
0 files removed
yum update pid: 33233
Docker CE Stable - x86_64                                                                                                                                                            0.0  B/s |   0  B     00:05    
Error: Failed to download metadata for repo 'docker-ce-stable': Librepo was interrupted by a signal

real	0m5.605s
user	0m0.507s
sys	0m0.106s

So the difference for single tests is 0.043s 😄 that is less than 1% and scripts are slightly different.

If you could give an example of a program that is "stopped/killed" slowly after running with sudo versus running as root without sudo I will be happy to investigate.

Best,
Alex

[millert]

@AlexBaranowski Thanks for testing. I'm closing this as it doesn't appear to be an issue with sudo.