Cannot read device /dev/loop0

Question

I'm trying to create a crypted drive on my loop0 device. For this command

/sbin/cryptsetup create cryptedDrive /dev/loop0

I'm getting the following error

Cannot read device /dev/loop0

Here's my strace output for the loop3 device:

(for a better paste -> pastebin)

munmap(0xb7845000, 4096)                = 0
mlockall(MCL_CURRENT|MCL_FUTURE)        = 0
getpriority(PRIO_PROCESS, 0)            = 20
setpriority(PRIO_PROCESS, 0, -18)       = 0
stat64("/dev/loop3", {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 3), ...}) = 0
open("/dev/loop3", O_RDONLY|O_SYNC|O_DIRECT|O_LARGEFILE) = 3
ioctl(3, BLKSSZGET, 0xbff2ad84)         = 0
fstatfs64(3, 84, {f_type=0x1021994, f_bsize=4096, f_blocks=46077, f_bfree=46033, f_bavail=46033, f_files=46077, f_ffree=45421, f_fsid={0, 0}, f_namelen=255, f_frsize=4096}) = 0
fstat64(3, {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 3), ...}) = 0
open("/proc/mounts", O_RDONLY)          = 4
fstat64(4, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7845000
read(4, "rootfs / rootfs rw 0 0\nnone /sys"..., 1024) = 873
stat64("/dev/shm", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=40, ...}) = 0
stat64("/var/run", {st_mode=S_IFDIR|0755, st_size=460, ...}) = 0
stat64("/var/lock", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=60, ...}) = 0
stat64("/lib/init/rw", {st_mode=S_IFDIR|0755, st_size=60, ...}) = 0
read(4, "", 1024)                       = 0
_llseek(4, 0, [0], SEEK_SET)            = 0
read(4, "rootfs / rootfs rw 0 0\nnone /sys"..., 1024) = 873
stat64("/", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
stat64("/sys", {st_mode=S_IFDIR|0755, st_size=0, ...}) = 0
stat64("/proc", {st_mode=S_IFDIR|0555, st_size=0, ...}) = 0
stat64("/dev", {st_mode=S_IFDIR|0755, st_size=3540, ...}) = 0
close(4)                                = 0
munmap(0xb7845000, 4096)                = 0
read(3, "", 512)                        = 0
write(2, "Cannot read device /dev/loop3.\n", 31Cannot read device /dev/loop3.
) = 31
close(3)                                = 0
munlockall()                            = 0
setpriority(PRIO_PROCESS, 0, 0)         = 0
exit_group(-22)                         = ?

(for a better paste -> pastebin)

Have you mapped a physical device to the loop device? What's the output of `losetup -a`? — MadHatter, Jul 13 '12 at 10:22

score 5 · Accepted Answer · answered Jul 13 '12 at 10:31

The lack of output from losetup -a, and that fact that losetup -f gives you the first free device as /dev/loop0, shows that you haven't yet associated that loopback device with any physical storage. What unused physical partition or LVM volume do you wish to use as the actual storage for your loopback encrypted device?

If it's, say, /dev/sd2a, then bind that to the loopback device with losetup /dev/loop0 /dev/sd2a, and try cryptsetup again.

Cannot read device /dev/loop0

1 Answers1