dd if=/dev/urandom of=/dev/hda2 bs=1M doesn't work

Melsync · 07-16-2006, 08:29 AM

I'm following the instructions to setup a loop device but I fail to fill a partition with random data.

Code:

dd if=/dev/urandom of=/dev/hda2 bs=1M

as root doesn't do anything, the command line stops there and nothing is written to /dev/hda2.

/etc/fstab mounts the device at boot:

Code:

/dev/hda2               /mnt/styo               vfat    user,defaults,umask=000 0 0

/mnt/styo remains unchanged.
Why? Thank you.

jlliagre · 07-16-2006, 09:32 AM

Use strace to find out what dd is (perhaps not) doing:

Code:

# strace dd if=/dev/urandom of=/dev/hda2 bs=1M

pixellany · 07-16-2006, 11:51 AM

How big is the partition that you are writing to? It may be that the command will take some time. Check and see that the disk access light starts flashing when you issue the command---that tells you that something is happening.

Matir · 07-16-2006, 12:20 PM

Also, make sure the disk is not mounted when you attempt this: that could cause a number of problems.

Melsync · 07-16-2006, 05:35 PM

/dev/hda2 is 60 GB big. I unmounted it. The command has been running for more than an hour now.
The output of strace dd if=/dev/urandom of=/dev/hda2 bs=1M is

Quote:

execve("/bin/dd", ["dd", "if=/dev/urandom", "of=/dev/hda2", "bs=1M"], [/* 24 vars */]) = 0
brk(0) = 0x9c27000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=144382, ...}) = 0
old_mmap(NULL, 144382, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7f07000
close(3) = 0
open("/lib/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\212~\177"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1485672, ...}) = 0
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f06000
old_mmap(0x417e3000, 1215452, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x417e3000
old_mmap(0x41906000, 16384, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x123000) = 0x41906000
old_mmap(0x4190a000, 7132, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x4190a000
close(3) = 0
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f05000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb7f056c0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
mprotect(0x41906000, 8192, PROT_READ) = 0
mprotect(0x4101a000, 4096, PROT_READ) = 0
munmap(0xb7f07000, 144382) = 0
brk(0) = 0x9c27000
brk(0x9c48000) = 0x9c48000
open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=49618608, ...}) = 0
mmap2(NULL, 2097152, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7d05000
close(3) = 0
close(0) = 0
open("/dev/urandom", O_RDONLY|O_LARGEFILE) = 0
close(1) = 0
open("/dev/hda2", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 1
rt_sigaction(SIGINT, NULL, {SIG_DFL}, 8) = 0
rt_sigaction(SIGINT, {0x80495cd, [], 0}, NULL, 8) = 0
rt_sigaction(SIGQUIT, NULL, {SIG_DFL}, 8) = 0
rt_sigaction(SIGQUIT, {0x80495cd, [], 0}, NULL, 8) = 0
rt_sigaction(SIGPIPE, NULL, {SIG_DFL}, 8) = 0
rt_sigaction(SIGPIPE, {0x80495cd, [], 0}, NULL, 8) = 0
rt_sigaction(SIGUSR1, NULL, {SIG_DFL}, 8) = 0
rt_sigaction(SIGUSR1, {0x8049638, [], 0}, NULL, 8) = 0
mmap2(NULL, 1060864, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7c02000
read(0, "\2\347\336\2648\n#\353\355\346\277\331\266\360{v\206\304"..., 1048576) = 1048576
write(1, "\2\347\336\2648\n#\353\355\346\277\331\266\360{v\206\304"..., 1048576) = 1048576
read(0, "g\t\356\311\2144\272\266\204q+\347\240\267\272)w\333Nj"..., 1048576) = 1048576
write(1, "g\t\356\311\2144\272\266\204q+\347\240\267\272)w\333Nj"..., 1048576) = 1048576

and the disk led keeps on blinking. The processor is an Athlon 1100 MHz

Matir · 07-16-2006, 05:49 PM

60GB will take quite a while. That shows that 2MB have been copied to the disk. How far along was that strace ouput captured?

jlliagre · 07-16-2006, 06:51 PM

And by the way, why are you filling this partition with random data ?

teckk · 07-16-2006, 06:53 PM

http://www.linuxquestions.org/questi...hreadid=366442

Let me add that.

Matir · 07-16-2006, 06:56 PM

Quote:

Originally Posted by jlliagre

And by the way, why are you filling this partition with random data ?

I'd guess (and I'm sure the OP will correct me) that he's either trying to thoroughly wipe a drive before selling it/giving it away or he's preparing to setup some sort of cryptoloop setup that would work better with a partition full of random data.