Your full file system is the problem. You must check for what happened to fill it up and then decide what to do about it so it will not happen again.
Check your /var/adm/messages file for possible clues - if you have access to SunSolve, search for "filesystem full" or "/ full no login"- It gives different possible problems - one may be this:
This is caused by a full file system and the system has no space
to write its utmpx (login info) entry.
To get around this condition the system must be booted up
into single user mode. Then clear (do not delete) the files:
/var/adm/utmp
/var/adm/utmpx
This can be done by typing:
#cat /dev/null > filename
This command will zero out the file but keep it there with
the correct permissions.
In some cases after removing these files your /var filesystem may
still be full. In this case type:
du -askd /var |sort -nr |more
This will give you a listing of the files from largest to smallest
on the /var filesystem.
In order to create space you may zero out the following files:
/var/cron/log
/var/spool/lp/logs
/var/adm/messages
You may also check the following for any large files that can be deleted:
/.wastebasket
/lost+found
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Subsequent logins should work fine after this.
Keywords: var, umptx, wtmpx, utmp, wtmp
full file system
changing a flat filesystem
