QA » openQA Project » openQA Tests

I discovered interesting behavior of script_output on spvm backend. When is script_output used for first, few lines at the beginning can be lost.
Here is the openQA reproduction:

• http://10.100.12.105/tests/1978#step/kdump_and_crash/5 script_output is used to get systemctl status kdump, but first lines are missing.

# Result:
  Process: 4248 ExecStart=/lib/kdump/load.sh --update (code=exited, status=0/SUCCESS)
 Main PID: 4248 (code=exited, status=0/SUCCESS)
    Tasks: 0 (limit: 4915)
   CGroup: /system.slice/kdump.service

• http://10.100.12.105/tests/1977#step/kdump_and_crash/7 one character was echoed to /dev/sshserial, script_output is used to get systemctl status kdump, all lines are captured

# Result:
F0ZS5
● kdump.service - Load kdump kernel and initrd
   Loaded: loaded (/usr/lib/systemd/system/kdump.service; enabled; vendor preset: disabled)
   Active: active (exited) since Mon 2019-05-06 16:37:24 EDT; 13h ago
  Process: 4248 ExecStart=/lib/kdump/load.sh --update (code=exited, status=0/SUCCESS)
 Main PID: 4248 (code=exited, status=0/SUCCESS)
    Tasks: 0 (limit: 4915)
   CGroup: /system.slice/kdump.service

I was able to manually reproduce similar behavior with named pipe on my system. Do it is root to have all output from systemctl,

• open first terminal

  mkfifo mypipe
  tail -f mypipe
  

• open second terminal

  systemctl status sshd | tee  mypipe
  

Result of first status command, initial lines are missing:

May 08 22:51:43 headcleaner.lan sshd[9215]: Accepted publickey for petr from x.x.x.x port 59408 xxx
May 08 22:51:43 headcleaner.lan sshd[9215]: pam_unix(sshd:session): session opened for user user by (uid=0)

Result of second use of status command:

● sshd.service - OpenSSH Daemon
   Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: disabled)
   Active: active (running) since Mon 2019-05-06 08:23:50 CEST; 4 days ago
 Main PID: 1467 (sshd)
    Tasks: 1
   Memory: 2.0M
   CGroup: /system.slice/sshd.service
           └─1467 /usr/sbin/sshd -D

If is reading from named pipe done by cat like, all lines are displayed.

cat mypipe

Maybe, we just need to flush buffer(like write something to it) in pipe before reading from it or maybe update os-autoinst part which reading from /dev/sshserial (in similar way like there is difference between cat and tail)?