You can cram it full, but note that /tmp and /var both need disk space for your operating system to function properly. Usually on a server setup you would have these directories on separate partitions. If you have these lumped together with / (which is recommended for desktop use), just be aware that you need some free space for temporary files, log files, and other such things.
If you are using default ext4 file system, no need to worry
By default 5% of the file system is reserved for the operating system to use. So you can fill your file system up to 95%, and the operating system can continue to work because it has this reserved disk space where it can put any temporary files, log files, and such.
If you have separate data partitions (for /home for example), you can use tune2fs to decrease or remove the reserved block count. Because on a data partition you generally don't need disk space reserved for the operating system to use. It needs disk space on /tmp and /var.
You can view the settings of your ext4 file system with (here as example for /dev/sdb1 partition):
Or just the reserved block count:
Code: Select all
sudo tune2fs -l /dev/sdb1 | grep 'Reserved block count'
To remove the 5% reserved blocks for a data partition, do: