I am running fedora 5.3.12-200.fc30.x86_64 and testing simple tcp client/server codes. I tried running different ps commands but I can not get any value displayed in wchan field, although in my case both server and client are in suspended states.
edited
After further testing it looks like it depends on distribution. Kali and devuan compute wchan value, while fedora and OpenSUSE Tumbleweed do not. Does anyone have a clue why that might be the case? Only entry in kernel that i found corresponds to wchan value
(CONFIG_SCHED_OMIT_FRAME_POINTER=y)
is configured the same way in kali, tumbleweed and fedora. I could not find that parameter in devuan.
Following is output of ps command on fedora. No matter what I do wchan only shows that process is running. I tried running different ps commads displaying all processes but wchan values never show anything else but hyphen.
$ ps -o pid,ppid,wchan=WIDE-WCHAN-COLUMN -o comm -o stat -t pts/6 -t pts/7
PID PPID WIDE-WCHAN-COLUMN COMMAND STAT
58565 4247 - bash Ss
102840 58565 - su S
102848 102840 - bash S
103048 4247 - bash Ss
122844 102848 - tcpserv01 S+
122848 103048 - tcpcli01 S+
122849 122844 - tcpserv01 S+
I checked wchan in /proc and all I get is 0.
$ cat /proc/122844/wchan
0
Server's strace does not pass accept() which is exactly what I expected.
# strace -p 122844
strace: Process 122844 attached
accept(3,
Client's strace is blocked at read() as expected.
# strace -p 122848
strace: Process 122848 attached
read(0,
But they don't show in wchan. What am I missing?
On a side note I also have FreeBSD (VM) on same machine and in FreeBSD 12.0-RELEASE wchan shows correctly when using ps command, so I am pretty sure this has something to do with fedora.
$ ps aux -o pid,wchan=WIDE-WCHAN-COLUMN -o comm -o stat
USER PID %CPU %MEM VSZ RSS TT STAT STARTED TIME COMMAND PID WIDE-WCHAN-COLUMN COMMAND STAT
root 11 599.0 0.0 0 96 - RNL 13:01 360:26.86 [idle] 11 - idle RNL
root 0 0.0 0.0 0 528 - DLs 13:01 0:00.01 [kernel] 0 swapin kernel DLs
root 1 0.0 0.0 9952 1016 - ILs 13:01 0:00.01 /sbin/init -- 1 wait init ILs
root 2 0.0 0.0 0 16 - DL 13:01 0:00.00 [crypto] 2 crypto_w crypto DL
EDIT I found following in man ps
-n Set namelist file. Identical to N. The namelist file is needed for a proper WCHAN display, and must match the current Linux kernel exactly for correct output. Without this option, the default search path for the namelist is: $PS_SYSMAP...
So I've set
PS_SYSMAP=/boot/System.map-$(uname -r)
But I still do not get any output from wchan. If I try running same command as before but with -n I get
$ ps -n -o pid,ppid,wchan=WIDE-WCHAN-COLUMN -o comm -o stat -t pts/2 -t pts/3 -t pts/4
PID PPID WIDE-WCHAN-COLUMN COMMAND STAT
4830 4829 - bash Ss
6201 4829 - bash Ss
6251 6201 - tcpserv01 S+
6252 4829 - bash Ss
6292 6251 - tcpse <defunct> Z+
6356 6252 - tcpcli01 S+
6357 6251 - tcpserv01 S+
6481 4830 - ps R+
With -n option wchan does not even show hyphen as before.
EDIT 2 Answer to following question is no. Kali's kernel configured that parameter exactly as fedora, but in Kali wchan values are computed. OpenSuse Tumbleweed behaves just like fedora, does not compute wchan values. Devuan computes wchan.
Could missing wchan values be due to
CONFIG_SCHED_OMIT_FRAME_POINTER: Single-depth WCHAN output
which in my kernel is configured as
CONFIG_SCHED_OMIT_FRAME_POINTER=y
