mysqld_safe holding open a pty/tty on FreeBSD (7.x and 8.x)

[Jeremy Chadwick]

Something interesting I've come across which happens on both RELENG_7
and RELENG_8 (indicating it's not a problem with the older tty code or
the newer pty/pts code), and it's reproducible on Linux (sort of...).

mysqld_safe appears to hold a pty/tty open even after the process has
been backgrounded.  I can understand how/why this might occur, just not
in this particular case.

I had a colleague test the situation on his Linux machine.  He was able
to confirm that:

1) "mysqld_safe > /dev/null 2>&1 &" never released the tty
2) "nohup mysqld_safe > /dev/null 2>&1 &" did release the tty

With regards to test #1, looking in /proc/{pid}/fd showed that STDIN was
being held open.  I recommended he point STDIN to /dev/null as so:

"mysqld_safe < /dev/null > /dev/null 2>&1 &"

Which also solved the problem.

On FreeBSD it's a different story.  Below, mysql-server was started as
root on pts/1.  The open file descriptors all point to /dev/null, so I'm
not sure why the pty/tty is being held open.

icarus# ps -aux -U mysql
USER    PID %CPU %MEM   VSZ   RSS  TT  STAT STARTED      TIME COMMAND
mysql 10078  0.2  0.3 35100 11032   1  S    11:38PM   0:00.02 [mysqld]
mysql  9997  0.0  0.0  8228  1592   1  S    11:38PM   0:00.01 /bin/sh /usr/local/bin/mysqld_safe --defaults-extra-file=/storage/mys
icarus# procstat -f 9997
  PID COMM               FD T V FLAGS    REF  OFFSET PRO NAME
 9997 sh                cwd v d --------   -       - -   /root
 9997 sh               root v d --------   -       - -   /
 9997 sh                  0 v c r-------   1       0 -   /dev/null
 9997 sh                  1 v c -w------   2       0 -   /dev/null
 9997 sh                  2 v c -w------   2       0 -   /dev/null
icarus# procstat -f 10078
  PID COMM               FD T V FLAGS    REF  OFFSET PRO NAME
10078 mysqld            cwd v d --------   -       - -   /storage/mysql
10078 mysqld           root v d --------   -       - -   /
10078 mysqld              0 v c r-------   1       0 -   /dev/null
10078 mysqld              1 v r rwa-----   1   32048 -   /storage/mysql/icarus.home.lan.err
10078 mysqld              2 v r rwa-----   1   32380 -   /storage/mysql/icarus.home.lan.err

At this point I log out of pts/1 and log back in to the machine (which
sticks me on pts/2 as a result of the problem).  Looking again, we see:

icarus# ps -aux -U mysql
USER    PID %CPU %MEM   VSZ   RSS  TT  STAT STARTED      TIME COMMAND
mysql  9997  0.0  0.0  8228  1592   1- I    11:38PM   0:00.01 /bin/sh /usr/local/bin/mysqld_safe --defaults-extra-file=/storage/mys
mysql 10078  0.0  0.3 35100 11032   1- I    11:38PM   0:00.02 [mysqld]

With absolutely no change in procstat output relevant to fds 0/1/2.
Yet pts/1 still appears held open by something:

icarus# ls -l /dev/pts
total 0
crw--w----  1 jdc   tty      0, 116 Sep 29 23:44 0
crw-rw-rw-  1 root  wheel    0, 115 Sep 29 23:41 1
crw--w----  1 jdc   tty      0, 117 Sep 29 23:44 2

fstat also shows no indication of anything using pts/1:

icarus# fstat /dev/pts/1
USER     CMD          PID   FD MOUNT      INUM MODE         SZ|DV R/W NAME
icarus# fstat | grep pts/1
icarus#

Ideas?

-- 
| Jeremy Chadwick                                   jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |