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What partition is root mounted on?
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Gentree
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Location: France, Old Europe

PostPosted: Fri Aug 09, 2013 9:04 am    Post subject: What partition is root mounted on? Reply with quote

This is not new but it's just annoyed me enough to try to find an answer.

Why do mount and df no longer tell we what partition root fs is mounted on. Isn't that kindof important info? Since the point of mount command is to tell me what is mounted and where , why does it hide that information for the most important partition on the system.
Code:

#dfh
Filesystem     Type     Size  Used Avail Use% Mounted on
rootfs         rootfs    14G   13G 1008M  93% /
/dev/root      ext4      14G   13G 1008M  93% /

mount
rootfs on / type rootfs (rw)
/dev/root on / type ext4 (rw,noatime,nodiratime,commit=0)


So all I get told now is some pseudo device /dev/root instead of where it really is, like physically.

If I'm going to pull out a disk I need to know where things REALLY are not pseudo device names.

What it is the idea behind this evasiveness and what commands still give me the vital information I need to administer the hardware?

TIA, Genree. 8)
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Navar
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Joined: 20 Aug 2012
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PostPosted: Fri Aug 09, 2013 11:07 am    Post subject: Reply with quote

I thought this was udev related, devtmpfs, or just plain kernel (VFS) changes. I forget and couldn't find some of the threads in the past regarding why mount was no longer indicating or resolving what was actual /.

So here's some quick possible alternatives (some may not work for fancier setups or other distros):

1. cat /proc/cmdline
2. ls -l /dev/root
3. dmesg | grep root=/

4. Or more low level,
Quote:

$ stat /
File: ‘/’
Size: 4096 Blocks: 8 IO Block: 4096 directory
Device: 808h/2056d Inode: 2 Links: 21
Access: (0755/drwxr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2013-07-03 02:20:21.742151254 -0600
Modify: 2013-07-03 03:51:57.945000682 -0600
Change: 2013-07-03 03:51:57.945000682 -0600
Birth: -

Or just stat -c %D /

Corresponds with major, minor values in /dev/sda8:
brw-rw---- 1 root disk 8, 8 Aug 8 13:38 sda8

You might also try busybox's rdev command, though that didn't seem functional for me (maybe wasn't built in).

Or mount may show you anyway as mine currently seems to be, rootfs -> / followed by next line having /dev/sda8 -> /. Same with df with 2 lines for rootfs and /dev/xyz -> /. Maybe you're using an initrd/initramfs?
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Navar
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PostPosted: Fri Aug 09, 2013 11:20 am    Post subject: Reply with quote

This isn't the thread I remember which I believe gave full reasoning behind why mount/df weren't showing actual /, but it still has some useful information:

https://forums.gentoo.org/viewtopic-t-689017-start-0-postdays-0-postorder-asc-highlight-.html
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Gentree
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PostPosted: Fri Aug 09, 2013 11:44 am    Post subject: Reply with quote

Thanks. Very helpful.

so bottom line is : to find the real root fs device:

Code:
ls -ail /dev/root


8)
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