strace
can attach and trace running processes. Check following simple example:
# cat dead_loop.c
#include <unistd.h>
int main(void)
{
while (1)
{
sleep(1);
}
return 0;
}
Build and launch two processes:
# gcc dead_loop.c -o dead_loop
# ./dead_loop &
[1] 2194
# ./dead_loop &
[2] 2195
Use -p
option to trace one process:
# strace -p 2194
strace: Process 2194 attached
restart_syscall(<... resuming interrupted nanosleep ...>) = 0
nanosleep({tv_sec=1, tv_nsec=0}, 0x7ffc037bf730) = 0
......
Use -p
option to trace multiple processes:
# strace -p 2194,2195
strace: Process 2194 attached
strace: Process 2195 attached
[pid 2194] restart_syscall(<... resuming interrupted nanosleep ...> <unfinished ...>
[pid 2195] restart_syscall(<... resuming interrupted nanosleep ...> <unfinished ...>
[pid 2194] <... restart_syscall resumed> ) = 0
[pid 2194] nanosleep({tv_sec=1, tv_nsec=0}, <unfinished ...>
[pid 2195] <... restart_syscall resumed> ) = 0
......
strace
can also utilize pidof
command to trace processes:
# strace -p "`pidof dead_loop`"
strace: Process 2195 attached
strace: Process 2194 attached
[pid 2194] restart_syscall(<... resuming interrupted nanosleep ...> <unfinished ...>
[pid 2195] restart_syscall(<... resuming interrupted nanosleep ...>) = 0
[pid 2195] nanosleep({tv_sec=1, tv_nsec=0}, <unfinished ...>
[pid 2194] <... restart_syscall resumed> ) = 0
......
Or use pgrep
:
# strace -p "`pgrep dead_loop`"
strace: Process 2194 attached
strace: Process 2195 attached
[pid 2195] restart_syscall(<... resuming interrupted nanosleep ...> <unfinished ...>
[pid 2194] restart_syscall(<... resuming interrupted nanosleep ...>) = 0
[pid 2194] nanosleep({tv_sec=1, tv_nsec=0}, <unfinished ...>
[pid 2195] <... restart_syscall resumed> ) = 0
[pid 2195] nanosleep({tv_sec=1, tv_nsec=0}, <unfinished ...>
......