限制 Unix 中的目录大小

Question

I am using my raspberry pi 4 with raspbian to host server. I have written some code that makes backups of the server data and I upload these to google drive using rclone. The problem is that I only have the 15 gb free plan on Google drive. I would want to limit the size of the local directory which I sync to Google drive to 15 gb. Is there a way to do this in Linux?

EDIT: I have understood that I am supposed to use Quota to do this. However Quota seems to be based on different users. At the moment I only have the standard user pi, is there a way to just limit the size of a certain backup directory with just the pi user.

Answer 1

Quotas in Linux work on a partition level: you can effectively limit a user to 15 GB worth of files on the root partition. That will also mean that the user's files will not exceed 15 GB in any given directory.

If the user owns files of significant size elsewhere, the target value of 15 GB will not be reachable. On the other hand, if the size of files owned by the user elsewhere is predictable, you could just add it to their quota: eg if you know the user owns a ~5 GB /home folder, you could set the quota to 20 GB, which will enable them to create 15 GB of backups. Obviously, if some of those 5 GB are subsequently removed, this will allow the user to exceed their 15 GB allowance for backups.

Quotas are really useful if you have lots of users to manage. If you want to limit the size of a single folder, better solutions exist. The best solution would be to add a check to your backup script which removes old backups until the backup folder is under 15 GB . Using quotas, or making a dedicated 15 GB backup partition, or a 15 GB file mounted to your backup folder, will all have the same drawback: your backup script will fail because of insufficient disk space, and you might end up with an incomplete backup.

Answer 2

Not sure how fast it would be but creating an .img file of 15GB and using it as mounted as storage will do exactly what you want.You can do all the normal things with it like create partitions format them if wanted.

root@zeus-H370M-DS3H:/home/zeus/qemu_vms# fdisk -l ubuntu-20.10-preinstalled-desktop-arm64+raspi.img 
Disk ubuntu-20.10-preinstalled-desktop-arm64+raspi.img: 8.15 GiB, 8750736384 bytes, 17091282 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xb6b5c3c7

Device                                             Boot  Start      End  Sectors  Size Id Type
ubuntu-20.10-preinstalled-desktop-arm64+raspi.img1 *      2048   526335   524288  256M  c W95 FAT32 
ubuntu-20.10-preinstalled-desktop-arm64+raspi.img2      526336 17091247 16564912  7.9G 83 Linux
root@zeus-H370M-DS3H:/home/zeus/qemu_vms# losetup -P /dev/loop0 ubuntu-20.10-preinstalled-desktop-arm64+raspi.img 
root@zeus-H370M-DS3H:/home/zeus/qemu_vms# mkdir /tmp/imgboot
root@zeus-H370M-DS3H:/home/zeus/qemu_vms# mkdir /tmp/imgroot
root@zeus-H370M-DS3H:/home/zeus/qemu_vms# mount /dev/loop0p2 /tmp/imgroot
root@zeus-H370M-DS3H:/home/zeus/qemu_vms# mount /dev/loop0p1 /tmp/imgboot
root@zeus-H370M-DS3H:/home/zeus/qemu_vms# ll /tmp/imgboot/
total 68870
-rwxr-xr-x 1 root root    26530 Oct 22 11:21 bcm2710-rpi-2-b.dtb
-rwxr-xr-x 1 root root    28028 Oct 22 11:21 bcm2710-rpi-3-b.dtb
snip.....
-rwxr-xr-x 1 root root 24222208 Oct 22 11:21 vmlinuz

root@zeus-H370M-DS3H:/home/zeus/qemu_vms# ll /tmp/imgroot/
total 1048660
lrwxrwxrwx   1 root root          7 Oct 22 11:00 bin -> usr/bin
drwxr-xr-x   4 root root       4096 Oct 22 11:12 boot
root@zeus-H370M-DS3H:/home/zeus/qemu_vms# rm -r /tmp/imgroot/*
root@zeus-H370M-DS3H:/home/zeus/qemu_vms# ll /tmp/imgroot/
total 0

You can do pretty much anything you want with them, how fast it would be as I say no clue.