How do I know ACLs are supported on my file system?

Is it enough to see getfacl giving no error, or do I have to check some other place to see whether or not ACLs are supported by the file systems?

Answers:

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Method 1

If you’re talking about a mounted filesystem, I don’t know of any intrinsic way to tell whether ACL are possible. Note that “are ACL supported?” isn’t a very precise question since there are several types of ACL around (Solaris/Linux/not-POSIX-after-all, NFSv4, OSX, …). Note that getfacl is useless as a test since it will happily report Unix permissions if that’s all there is: you need to try setting an ACL to test.

Still on mounted filesystem, you can check for the presence of acl in the mount options (which you can find in /proc/mount). Note that this isn’t enough: you also need to take the kernel version and the filesystem type in consideration. Some filesystem types always have ACL available, regardless of mount options; this is the case for tmpfs, xfs and zfs. Some filesystems have ACL unless explicitly excluded; this is the case for ext4 since kernel 2.6.39.

Method 2

To know if ACL is available you can:

1. Check current kernel version and filesystem:

   uname -r

   df -T or mount | grep root

   Recent distro have ACL mount option included by default (since kernel 2.6). So it’s not mandatory to redefine it in /etc/fstab (or similar). Non exhaustive list of filesystems concerned: ext3, ext4, tmpfs, xfs and zfs .

   If you have older setup then you may have to recompile the kernel and/or add acl in /etc/fstab.
   fstab example: /dev/root / ext4 acl,errors=remount-ro 0 1

2. Look for existing ACL settings (the “usual” config place is on /boot):

   sudo mount | grep -i acl #optionnal

   cat /boot/config* | grep _ACL

   Depending of the system you could find the settings in /procinstead. Here is a way to extract the config from the .gz archive and then search for acl settings:

   cat /proc/config.gz | gunzip > running.config && grep -i 'acl' running.config

   cat running.config | grep _ACL

   You should see something like:

   CONFIG_EXT3_FS_POSIX_ACL=y

   CONFIG_EXT2_FS_POSIX_ACL=y

   CONFIG_XFS_POSIX_ACL=y

   For the filesystem you can try to get more info with:

   sudo tune2fs -l /xxx/xxx| grep 'Default mount options:'

   (replace xxx/xxx by your filesystem)

—
Helpfull information can be found on:

– superuser.com,

– serverfault,

– bencane.com,

– wiki.archlinux.org

Method 3

acl should be enabled as default if you are using ext2/3/4 or btrfs.

Check with:

tune2fs -l /dev/sdXY | grep "Default mount options:"

If it isn’t in the output do a:

tune2fs -o acl /dev/sdXY

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0