FreeNX NX Startup Session Failed

Occasionally users are unable to connect to our FreeNX server, they report an error "Startup Session Failed". Clicking on "Detail" shows that it is unable to find the server session file.

Searching for solutions suggested a number of options, including removing the server /tmp/.X1\*\*\*-lock files, or simply removing FreeNX and installing NoMachine's NXServer instead.

In the end the solution proved remarkably simple:

On the server run:

# nxserver --list
NX> 100 NXSERVER - Version 1.5.0-60 OS (GPL)
NX> 127 Sessions list:
Display Username Remote IP Session ID
------- --------------- --------------- --------------------------------
1001 chris  1BC6B4B9C3CF4C2B6BD7137AC7FDE5DA
1000 helen -             87443D16622EC0751551685A93DD023B
1002 michelle DBAC430C8AA8B414A5E2228970E2BBDC
NX> 999 Bye

The session with no remote IP is for a session that has not ended properly. Terminate this session and users should be able to log in once again:

# nxserver --terminate helen

Update: This problem was little more complex than I at first thought, all I had really done is allow one more user to login before the issue re-occurred. You also need to check is that there are no old lock files in /tmp/.X11-unix:

# cd /tmp/.X11-unix
#ls -al
/tmp/.X11-unix# ls -al
total 316
drwxrwxrwt   2 root root      4096 2014-01-02 12:48 .
drwxrwxrwt 375 root root    315392 2014-01-02 12:48 ..
srwxrwxrwx   1 root root         0 2013-07-24 17:04 X0
srwxrwxrwx   1 helen helen       0 2014-01-02 10:32 X1000
srwxrwxrwx   1 chris chris       0 2014-01-02 11:42 X1001
srwxrwxrwx   1 michelle michelle 0 2014-01-02 08:52 X1002
srwxrwxrwx   1 terry  terry      0 2013-09-05 15:05 X1003

Notice that there is a .X11-unix file for terry X1003, but no corresponding user shown in nxserver --list above. Remove this spurious file and it should now work.

It would also make sense to ensure that the correct /tmp/.X1***-lock files are present:

# cd /tmp
# ls -al | grep -i X.*-lock
-rw------- 1 nx nx              0 2014-01-02 10:32 .nX1000-lock
-rw------- 1 nx nx              0 2014-01-02 11:42 .nX1001-lock
-rw------- 1 nx nx              0 2014-01-02 08:52 .nX1002-lock
-r--r--r-- 1 helen helen       11 2014-01-02 10:32 .X1000-lock
-r--r--r-- 1 chris chris       11 2014-01-02 11:42 .X1001-lock
-r--r--r-- 1 michelle michelle 11 2014-01-02 08:52 .X1002-lock

You should expect to see  the correct number of lock files for your user sessions,  in my case these required no changes, but if there had been spurious files, removing them would seem sensible.

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