Linux – pivot_root device or resource busy

linux

The following commands on Ubuntu 64bit on VMWare:

mount /dev/sda1 /newroot
cd /newroot
mkdir old-root
pivot_root . old-root

produce an error that I do not understand:

pivot_root: device or resource busy

Any ideas what might be the reason for that?

Edit: strace result

`strace pivot_root . old-root 
execve("/usr/sbin/pivot_root", ["pivot_root", ".", "old-root"], [/* 67 vars */]) = 0
brk(0)                                  = 0x77e000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2df4135000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=124467, ...}) = 0
mmap(NULL, 124467, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f2df4116000
close(3)                                = 0
open("/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0p\36b\0075\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=2096496, ...}) = 0`

Best Answer

You should unmount the /proc file system first and then execute your original set of commands.

umount /proc
mount /dev/sda1 /newroot
cd /newroot
mkdir old-root
pivot_root . old-root

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The way to check is fuser -vm /mnt/dir, which must be run as root. It will tell you which processes are accessing the mount point.

An alternative is lsof /mnt/dir, which will show each open file on the mount. Again best run as root.

You can run either of these as non-root, but then the output will be limited to your processes—ones from other users will just be silently not shown, even though they will prevent unmounting the filesystem.

Example:

Watt:~# fuser -vm /mnt/Zia/src
                     USER        PID ACCESS COMMAND
/mnt/Zia/src:        root     kernel mount /mnt/Zia/src
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The "access" field tells you how its being accessed. In this case, the kernel has it in use as a mount (duh, but unmount will be OK with only this). bash has it as the current working directory (will have to cd to a different directory before unmount) and gvim both has the current directory and has a file open (will need to close that gvim).

Watt:~# lsof /mnt/Zia/src
COMMAND   PID    USER   FD   TYPE DEVICE SIZE/OFF    NODE NAME
bash    24909 anthony  cwd    DIR   0,26    12288 3527682 /mnt/Zia/src/perl (zia.vpn.home:/home/anthony/src)
gvim    25041 anthony  cwd    DIR   0,26    12288 3527682 /mnt/Zia/src/perl (zia.vpn.home:/home/anthony/src)
gvim    25041 anthony    6u   REG   0,26    16384 3526219 /mnt/Zia/src/perl/.utf8.c.swp (zia.vpn.home:/home/anthony/src)

In this output, you can see the current directories for both bash and gvim (as type DIR). You can also see which file gvim has open for write.

How to force the issue:

fuser has a -k option which will send a signal (default: SIGKILL) to each process using the mount. This is a rather forceful way to stop the mount from being busy. (And of course, be careful of what you SIGKILL!)

umount has an -l option to perform a lazy unmount. The mount will be removed from the filesystem namespace (so you won't see it under /mnt/Zia/src anymore, in the example) but it stays mounted, so programs accessing it can continue to do so. When the last program accessing it exits, the unmount will actually occur.

There is one final fixable cause of unmount failing, and that's an NFS server going down. Here you can use umount -f, but you risk data loss if you do so. (The client may have cached writes that haven't been confirmed by the server yet, and those writes will be discarded. Apps, however, have already been told the write is successful.)

Linux – GNU/Linux: “device mapper: create ioctl failed” “device or resource busy”

First install 7.1a (if you can find it anymore) was the latest totally working version of truecrypt. You might try to install that and see if it fixes your problem.

However, this product is now basically obsolete as the developers have apparently stopped development of truecrypt for reasons not yet really fully understood. The current release 7.2 contains only a DECRYPT and not any of the encrypt functionality.

I'd be thinking seriously of shifting away from this project to something else. Although, I don't have a good feel on what that will be.

Best Answer

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