Has anyone seen this issue with the /dev/null?


 
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Top Forums UNIX for Advanced & Expert Users Has anyone seen this issue with the /dev/null?
# 1  
Old 09-18-2002
Question Has anyone seen this issue with the /dev/null?

hello all,
I am working in a Hpux 11.0 64 bit environment. I am not sure if a third party software is doing this or not, but the admin to this server says it is not a server issue as he has check and double check logs and crons to verify this issue. My problem, is that every now and then, once and hour or so, the /dev/null device gets its permissions changed to read only.... As you know, this can be a big head-ache for a lot of processes and apps that use this particuar device. One major software that we are seeing a lot of incidents with is Oracle. It uses the /dev/null a lot and whenever the permissions gets changed, Oracle complains. I am also getting this message when I log into the server every now and then. So to work around this issue, the sysadmin has a cron that goes out and checks the permissions on the /dev/null device....but unfortunately cron only runs to the minute level and I need this to run at least every 3-5 seconds as we have files processing against Oracle constantly 24 X 7.....and I am not really comfortable with band aid approaches......Does anyone have any recommendations. This is starting to be a big issue for me now that this server is starting to be utilize a lot more than before...

thanks,
OS
# 2  
Old 09-18-2002
On my HP-UX systems, I see that /dev/null is owned by bin. This means that either bin or root could change the mode. I would chown /dev/null to root and let it change modes again. If it does, you know the process was a root process.

Make sure that no one is signed on as root or su'ed to root. If it changes, either a running process or a cronjob did it.

"ls -lc /dev/root" will get the exact time of change. Check every cron job that was running during the change. The periodic nature of the problem also is pointing to a bad cron job.
# 3  
Old 09-18-2002
might be overkill but...

If necessary, You may need to remove it and then recreate it to restore ownwership and permissions.

This may be overkill, but might be necessary.

Make sure to note the minor number before you do this.

Smilie
# 4  
Old 09-18-2002
Data

My question on the file ownership changes.....since /dev/null permissions are set to rw-rw-rw and owned by bin, even if I change ownership over to root, wouldn't a process still be able to change the user level permissions on this device......to read only...and look like this afterwards, rw-rw-r--. since the user level permission is set to rw-.

thanks for the feedback...

OS
# 5  
Old 09-18-2002
You must own a file or be root to change the mode of the file. Try it.
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