strace
strace is an important utility to query system call usage.tracing a running process
strace -p $PID
Get a process's system call category report
Use strace -cstrace -p 3712 -c Process 3712 attached - interrupt to quit Process 3712 detached % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 94.27 0.006843 3 2641 poll 4.16 0.000302 0 7781 gettimeofday 1.20 0.000087 1 70 futex 0.37 0.000027 0 5244 ioctl 0.00 0.000000 0 510 read 0.00 0.000000 0 233 write ------ ----------- ----------- --------- --------- ---------------- 100.00 0.007259 16479 total
Tracing a hung process
Do a strace -p on the process, if it ends with
read(13,
That means the system is hung on a read system call, to the file descriptor 13. Do a lsof to find out what fd #13 is.
