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My question is pretty simple but another opinion would be nice. We have Debian [2.6.18-6-686] machine, /home is mapped like this

df -h | grep home
/dev/mapper/local_disc-home
                      6,0G  5,1G  580M  90% /home

There are around 150 users folders in /home. My question is, what would happen if usage gets 100 percent. No user will be able to login and all logged users will lost terminals? Or there is some safety mechanism to keep sessions allive? If I understand this right every one user can full up the /home and that will affect all users.

Thx for answers

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2 Answers

up vote 2 down vote accepted

what would happen if usage gets 100 percent. No user will be able to login and all logged users will lost terminals?

Generally, yes, if /home fills up the system will become largely unusable. People will probably not lose their existing terminal sessions, but they will be effectively dead in the water since they will not be able to create any more files.

New logins will generally fail because many tools want to write data into your home directory as part of the login process. Simple command-line logins (e.g., using ssh) may succeed but the system won't be particularly useful.

If I understand this right every one user can full up the /home and that will affect all users.

This is why many storage administrators implement filesystem quotas...to prevent users from filling up a shared filesystem. If you have 150 users and only 6GB of space, you want to make sure that no single user can use more than 40MB of space if you want to evenly distribute disk space.

You may also want to purchase additional disk space and expand the filesystem, because it sounds like you're oversubscribed given the number of users and the available space.

Here is an article that talks about using quotas in Linux.

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In addition to larsks' answer: this is the reason why there is a percentage of reserved blocks when you create the file system (or tune it later). These reserved blocks can only be used by the super-user. You could consider this a buffer before even root will be unable to log into the system and rectify the situation.

From mkfs.ext3(8):

-m reserved-blocks-percentage

Specify the percentage of the filesystem blocks reserved for the super-user. This avoids fragmentation, and allows root-owned daemons, such as syslogd(8), to continue to function correctly after non-privileged processes are prevented from writing to the filesystem. The default percentage is 5%.

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