df: rows appear in different order on each execution, but shouldn't

[jfinkels]

Running df with no other arguments results in a different order of rows on each execution. In contrast, the GNU version of df seems to produce rows in the same order on each execution.

GNU df:

$ df | head -n 5
Filesystem                1K-blocks     Used Available Use% Mounted on
udev                        3858028        0   3858028   0% /dev
tmpfs                        782624     2112    780512   1% /run
/dev/mapper/vgubuntu-root 242791844 93491652 136897300  41% /
tmpfs                       3913120        0   3913120   0% /dev/shm
$ df | head -n 5
Filesystem                1K-blocks     Used Available Use% Mounted on
udev                        3858028        0   3858028   0% /dev
tmpfs                        782624     2112    780512   1% /run
/dev/mapper/vgubuntu-root 242791844 93491652 136897300  41% /
tmpfs                       3913120        0   3913120   0% /dev/shm

uutils df:

$ ./target/debug/df | head -n 5
Filesystem          1k-blocks         Used    Available  Use% Mounted on       
/dev/loop5           56885248     56885248            0  100% /snap/snap-store/558
/dev/nvme0n1p1      535805952     32583680    503222272    6% /boot/efi       
/dev/loop1           58327040     58327040            0  100% /snap/core18/2284
tmpfs               801406976        73728    801333248    0% /run/user/1000  
$ ./target/debug/df | head -n 5
Filesystem          1k-blocks         Used    Available  Use% Mounted on       
/dev/loop4           65011712     65011712            0  100% /snap/core20/1270
tmpfs              4007034880            0   4007034880    0% /sys/fs/cgroup  
tmpfs              4007034880            0   4007034880    0% /dev/shm        
/dev/loop0           58195968     58195968            0  100% /snap/core18/2253

[tertsdiepraam]

Do you have any idea what GNU's order is based on?

[jfinkels]

On my Linux machine, It seems like it is based on the order given in /proc/mounts or /etc/mtab. The uucore::fsext::read_fs_list() function reads those:

coreutils/src/uucore/src/lib/features/fsext.rs

Lines 403 to 406 in 1f7c08d

	let (file_name, f) = File::open(LINUX_MOUNTINFO)
	.map(|f| (LINUX_MOUNTINFO, f))
	.or_else(|_| File::open(LINUX_MTAB).map(|f| (LINUX_MTAB, f)))
	.expect("failed to find mount list files");

but the df::filter_mount_list() collects them into a HashMap:

coreutils/src/uu/df/src/df.rs

Line 187 in 1f7c08d

HashMap::<String, Cell<MountInfo>>::new(),

so the order is lost.

[tertsdiepraam]

Good to know! Thanks!