Create a ramdisk for tmp and cache folders with persistent saves amoung reboots - with systemd.
Two different behaviors are explained below: how to mount the /tmp folder in a ramdisk, and how to mount cache folders in a ramdisk. These are different because what is in /tmp is meant to be destroyed on reboot, while you want to keep the cache amoung reboot to improve the responsiveness of your system.
I also mount the /var/log folder into a ramdisk, which has no performance improvement, but save the SDD as we write fewer on it. If you don't need it, a section tells you how to remove it.
This is a simple setup I use for my computer, don't hesitate to contribute to make it eaily usable by anyone.
Quick not about tmpfs: it is a filesystem integrated in the Linux kernel. If you mount such a filesystem in a folder, everything written in this folder will in fact be written in the RAM, thus lost after reboot.
By default, when you mount a tmpfs filesystem, it has a max size correspondig to half of your amount of RAM. What you need to understand is that tmpfs will only use the RAM it needs: if you create one file of 100 Mio in it, it will only take 100 Mio in the RAM.
However, if you try to write more than the limit, you will have a disk full error.
So, on a system with 32 Gio of RAM, it is totally possible to have multiple tmpfs mounted with a max size of 16 Gio. Though, you should be careful: if the RAM get full, it will start to swap (on the SSD? depending on your configuration) and your system may die (a reboot will save you).
This is the most important and usefull: the temporary files stored here are supposed to be removed on reboot.
Well... They are supposed to be removed as soon as a software don't use it anymore, but quite often, developpers forget to remove it...
If you store it in RAM, this purge will be automatically done.
Systemd mount this folder in RAM by default. If you are lucky, you don't have anything to do. To check, run the command df -hT:
$ df -hT
Sys. de fichiers Type Taille Utilisé Dispo Uti% Monté sur
udev devtmpfs 16G 0 16G 0% /dev
tmpfs tmpfs 3,2G 9,6M 3,2G 1% /run
/dev/nvme0n1p6 ext4 183G 5,4G 168G 4% /
tmpfs tmpfs 16G 0 16G 0% /dev/shm
tmpfs tmpfs 5,0M 4,0K 5,0M 1% /run/lock
tmpfs tmpfs 16G 0 16G 0% /sys/fs/cgroup
tmpfs tmpfs 16G 44K 16G 1% /tmp
tmpfs tmpfs 16G 127M 16G 1% /var/cache
tmpfs tmpfs 16G 38M 16G 1% /var/log
/dev/nvme0n1p5 ext4 233M 24M 193M 11% /boot
/dev/nvme0n1p2 vfat 95M 25M 71M 27% /boot/efi
/dev/nvme0n1p7 ext4 262G 47G 202G 19% /home
tmpfs tmpfs 16G 58M 16G 1% /home/sid/.mozilla
tmpfs tmpfs 16G 434M 16G 3% /home/sid/.cache
/dev/nvme0n1p4 fuseblk 500G 93G 407G 19% /mnt/w10
/dev/sda2 fuseblk 924G 287G 637G 32% /mnt/data
/dev/sda3 ext4 7,9G 691M 6,8G 10% /mnt/persistent
tmpfs tmpfs 3,2G 0 3,2G 0% /run/user/114
tmpfs tmpfs 3,2G 12K 3,2G 1% /run/user/1000All the lines with a tmpfs filesystem are mounted on the RAM. So, if you have the line
tmpfs tmpfs 16G 120K 16G 1% /tmp
your /tmp folder is already mounted in the RAM \o/ you don't have to do the following steps.
On Debian in particular, this behavior has been switched off... To reenable it, it is quite easy, just run the following commands as root:
# ln -s /usr/share/systemd/tmp.mount /etc/systemd/system/
# ln -s /dev/null /etc/tmpfiles.d/tmp.conf
# systemctl enable tmp.mount
The second command remove the default behavior of Debian which is remove everything in /tmp on boot, but you don't need it anymore thanks to the ramdisk.
Reboot and voilà!
You have 2 cache folders: the system one in /var/cache and the user one in /home/$USER/.cache. We will also take care of the logs in /var/log along with the firefox session folder. If you don't want it, check the last subsection of this section.
We need to distinguish 2 types of folders here: the system folders and the user folders. The user folders will be mounted later in the boot, while the system folders will be mounted as soon as possible. For me, it takes 1 minute to load user data.
The first file to change is home-sid-.cache.mount as your user is certainly not named sid.
In the section Unit, change the key ConditionPathIsSymbolicLink=, in the Mount section, change the key Where with your path (change the name of the user):
ConditionPathIsSymbolicLink=!/home/{USER}/.cache
...
Where=/home/{USER}/.cache
You also need to change the filename so it sticks to the path. To do so, you can generate the name of the file with:
$ systemd-escape -p --suffix=mount "/home/{USER}/.cache"
home-{USER}-.cache.mountnow you can simply
$ mv home-sid-.cache.mount home-{USER}-.cache.mountSame as in the previous section.
In the section [Unit], change the key RequiresMountsFor:
RequiresMountsFor=/home/{USER}/.cache /home/{USER}/.mozilla
You need to change the ramdisks variable with your paths:
declare -A ramdisks=(
["cache"]="/var/cache /mnt/persistent/system"
["log"]="/var/log /mnt/persistent/log"
["usercache"]="/home/sid/.cache /mnt/persistent/home"
["firefoxsession"]="/home/sid/.mozilla /mnt/persistent/firefox"
)Here, we assume that everything will be saved into a partition mounted in /mnt/persistent. You can save it in your home if you want, though you shouldn't store root data in your home... Anyway, be sure that the filesystem for the persistency is NOT NTFS but a Linux thing like ext4, or you will destroy the permissions... It is also recommended to mount it with the following permissions, as it should be just a backup: defaults,nodev,noexec,nosuid,noatime,nodiratime.
Now that everything is correctly configured, we need to install everything in the right folders. This can be done with the following commands run as root:
# cp ramdisk_cache.sh /usr/local/sbin/
# chmod u+x /usr/local/sbin/ramdisk_cache.sh
# cp systemramdisk.service /etc/systemd/system/
# cp userramdisk.service /etc/systemd/system/
# cp var-cache.mount var-log.mount home-{USER}-.cache.mount home-{USER}-.mozilla.mount /usr/share/systemd/
# ln -s /usr/share/systemd/var-cache.mount /etc/systemd/system/var-cache.mount
# ln -s /usr/share/systemd/var-log.mount /etc/systemd/system/var-log.mount
# ln -s /usr/share/systemd/home-{USER}-.cache.mount /etc/systemd/system/home-{USER}-.cache.mount
# ln -s /usr/share/systemd/home-{USER}-.mozilla.mount /etc/systemd/system/home-{USER}-.mozilla.mount
# systemctl daemon-reload
# systemctl enable var-cache.mount var-log.mount home-{USER}-.cache.mount home-{USER}-.mozilla.mount systemramdisk.service userramdisk.service
Before rebooting, we need to save the cache (and check everything works :p), so run ramdisk_cache.sh cache log usercache firefoxsession as root and check that your persistent folders are filled with the correct data.
We also need to setup a cron so the script is run every X minutes (here every hour but you can change), so you don't lose too much if your system crashes:
# crontab -e
0 * * * * /usr/local/sbin/ramdisk_cache.sh cache log usercache firefoxsession
systemctl disable var-log.mountAt the install step, don't copy, link or enable the file var-log.mount.
In the section Unit of systemramdisk.service, change the keys Before and RequiresMountsFor. If you already installed it, do the changes to the file /etc/systemd/system/systemramdisk.service:
Before=sysinit.target shutdown.target
...
RequiresMountsFor=/var/cache
Remove everything related to logs. If you already did the install, change the file /usr/local/sbin/ramdisk_cache.sh.
Finish by executing systemctl daemon-reload as root.
In the same way, edit the files corresponding to the user ramdisks if you don't want it.
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