GrepUpgradeBreaksDevPts

From NAS-Central Buffalo - The Linkstation Wiki

Latest revision as of 00:32, 11 November 2007

If you upgrade from the firmware's grep to one of the newer packaged ones floating around, you might find that all of a sudden your telnetd and sshd services don't work. Typical symptoms of the error:

 $ telnet tera
 Trying 192.168.11.150...
 Connected to tera.
 Escape character is '^]'.
 telnetd: getpty: No such file or directory
 .
 Connection closed by foreign host.

or

 Jul  1 17:35:49 HD-HTGLD03 sshd[8255]: error: openpty: No such file or directory
 Jul  1 17:35:49 HD-HTGLD03 sshd[8255]: error: session_pty_req: session 0 alloc failed
 Jul  1 17:35:49 HD-HTGLD03 sshd[8257]: error: setlogin failed: Function not implemented

This is most likely because devpts isn't being correctly mounted on /dev/pts any more. Let's take a close look at /etc/init.d/devpts.sh:

 devpts_avail=$(grep -qci '[<[:space:]]devpts' /proc/filesystems || true)
 devpts_mounted=$(grep -qci '/dev/pts' /proc/mounts || true)
 devfs_mounted=$(grep -qci '[<[:space:]]/dev[>[:space:]].*devfs' /proc/mounts || true)

Look at the impact of upgrading grep:

 root@HD-HTGLD03 ~ # grep devpts /proc/filesystems
 nodev   devpts
 root@HD-HTGLD03 ~ # ./grep.old -qci devpts /proc/filesystems
 1
 root@HD-HTGLD03 ~ # grep -qci devpts /proc/filesystems
 root@HD-HTGLD03 ~ #

Oops! The new grep has different behaviour with respect to -qc: it assumes (correctly) that the user does not want any output. This devpts.sh script relies on the dodgy behaviour of the old grep which still issues a match count even when -q is specified.

The fix is to remove the -q switch from the script:

 devpts_avail=$(grep -ci '[<[:space:]]devpts' /proc/filesystems || true)
 devpts_mounted=$(grep -ci '/dev/pts' /proc/mounts || true)
 devfs_mounted=$(grep -ci '[<[:space:]]/dev[>[:space:]].*devfs' /proc/mounts || true)

--Aspiers 19:21, 1 July 2007 (CEST)