Move /tmp to RAM

mountramtmpfs

I am trying to move /tmp to RAM and obey good practice:

/var/tmp should NOT be placed in tmpfs, as it must survive reboots
not mount /tmp as a stand-alone tmpfs, but rely on /dev/shm or /run/shm

However, things have changed between 2.6 and 3.2 kernels :

Changes to the configuration and defaults of tmpfs filesystems

On 3.2 kernel, use RAMTMP=yes in /etc/default/tmpfs.

My question is: how can I achieve this goal with older kernels ?

My choice is nor to modify /etc/fstab neither this :

mkdir /dev/shm/tmp
chmod 1777 /dev/shm/tmp
mount --bind /dev/shm/tmp /tmp

Is there something like RAMTMP for 2.6 kernels ?

Best Answer

You don't have to do all that, you can just mount /tmp as tmpfs by using a line like the following in /etc/fstab:

tmpfs /tmp tmpfs mode=1777,nosuid,nodev 0 0

You can also do it live (but bear in mind stuff that is currently in /tmp on your current filesystem will not be able to be accessed except through the inode and currently open file descriptors, so you should really do this by modifying /etc/fstab and rebooting):

mount -o mode=1777,nosuid,nodev -t tmpfs tmpfs /tmp

Note that a tmpfs can swap. If you want a truly RAM-only filesystem, use ramfs.

Related Solutions

How to make tmpfs to use only the physical RAM and not the swap

use ramfs instead of tmpfs. ramfs is a ramdisk (no swap) tmpfs can be both in your /etc/fstab:

none     /path/to/location     ramfs  defaults,size=512M   0     0

edit the size parameter to whatever you like but be careful not to exceed your actual amount of ram.

NOTE: the use of a ramfs instead of tmpfs is not something i would recommend. you will find yourself experiencing stability issues if something happens and you write a ton of data to your ramdisk. you can NOT unallocate ram from a ramfs. once your ramdisk (all of your ram) is full your system will seize up. ram is volatile memory, meaning once it looses power all data is gone. so if your ramdisk fills up your ram and you crash you will never see what was on your ram disk again. unlike ramfs, tmpfs limits its size.

Linux – Does tmpfs automatically resize when the amount RAM changes, and does it compete when there’s multiple tmpfs

If you mount a tmpfs instance with a percentage it will take the percent size of the systems physical ram. For instance, if you have 2gb of physical ram and you mount a tmpfs with 50%, your tmpfs will have a size of 1gb. In your scenario, you add physical ram to your system, let's say another 2gb, that your system has 4gb of physical ram. When mounting the tmpfs it will have a size of 2gb now.

When mounting multiple instances of tmpfs each with 50% set, it will work. If both tmpfs instances were filled completely, the system will swap out the lesser used pages. If swap space is full too, you will have No space left on device errors.

Edit:

tmpfs only uses the amount of memory that is taken, not the full 50%. So, if only 10mb of those 1gb are taken, your tmpfs instance only occupies those 10mb. It's not not reserved, it's dynmically. With multiple instances of 50%, the first one that need memory gets memory. The system swapps the lesser used pages, if 50% is occupied or not. The tmpfs instance is not aware of the fact whether it uses physical ram or swap space. You can mount a tmpfs of 100gb if you want and it will work.

I assume that you shut the system down before adding ram. So the tmpfs is remounted at startup anyway. If you add ram while the system runs, you will fry the ram, the motherboard and most likely your hand. I can't really recommand that :-)

Sources:

Kernel Documentation

Best Answer

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How to make tmpfs to use only the physical RAM and not the swap

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