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.

jrojsh · 05-18-2014, 08:27 PM

i managed to strace my dd while it was running, although id appreciate some help deciphering what its really doing here...5 hours running doing something i think...

Quote:

strace dd if=/dev/urandom of=/dev/sda bs=1M
execve("/bin/dd", ["dd", "if=/dev/urandom", "of=/dev/sda", "bs=1M"], [/* 47 vars */]) = 0
brk(0) = 0xbfb000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f61700cb000
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=90307, ...}) = 0
mmap(NULL, 90307, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f61700b4000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320\37\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1845024, ...}) = 0
mmap(NULL, 3953344, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f616fae5000
mprotect(0x7f616fca1000, 2093056, PROT_NONE) = 0
mmap(0x7f616fea0000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1bb000) = 0x7f616fea0000
mmap(0x7f616fea6000, 17088, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f616fea6000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f61700b3000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f61700b1000
arch_prctl(ARCH_SET_FS, 0x7f61700b1740) = 0
mprotect(0x7f616fea0000, 16384, PROT_READ) = 0
mprotect(0x60c000, 4096, PROT_READ) = 0
mprotect(0x7f61700cd000, 4096, PROT_READ) = 0
munmap(0x7f61700b4000, 90307) = 0
rt_sigaction(SIGUSR1, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGINT, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGUSR1, {0x403c90, [INT USR1], SA_RESTORER, 0x7f616fb1bff0}, NULL, 8) = 0
rt_sigaction(SIGINT, {0x403c80, [INT USR1], SA_RESTORER|SA_NODEFER|SA_RESETHAND, 0x7f616fb1bff0}, NULL, 8) = 0
brk(0) = 0xbfb000
brk(0xc1c000) = 0xc1c000
open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=2919792, ...}) = 0
mmap(NULL, 2919792, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f616f81c000
close(3) = 0
open("/dev/urandom", O_RDONLY) = 3
dup2(3, 0) = 0
close(3) = 0
lseek(0, 0, SEEK_CUR) = 0
open("/dev/sda", O_WRONLY|O_CREAT|O_TRUNC, 0666) = -1 EACCES (Permission denied)
open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=2570, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f61700ca000
read(3, "# Locale name alias data base.\n#"..., 4096) = 2570
read(3, "", 4096) = 0
close(3) = 0
munmap(0x7f61700ca000, 4096) = 0
open("/usr/share/locale/en_US.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en_US.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en_US/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en_US.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en_US.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en_US/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en/LC_MESSAGES/coreutils.mo", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=619, ...}) = 0
mmap(NULL, 619, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f61700ca000
close(3) = 0
open("/usr/lib/charset.alias", O_RDONLY|O_NOFOLLOW) = -1 ENOENT (No such file or directory)
write(2, "dd: ", 4dd: ) = 4
write(2, "failed to open \342\200\230/dev/sda\342\200\231", 29failed to open ‘/dev/sda’) = 29
open("/usr/share/locale/en_US.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en_US.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en_US/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en_US.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en_US.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en_US/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
write(2, ": Permission denied", 19: Permission denied) = 19
write(2, "\n", 1
) = 1
close(2) = 0
exit_group(1) = ?
+++ exited with 1 +++
jro@jro-System-Product-Name ~ $

Emerson · 05-18-2014, 09:01 PM

/dev/urandom can be (and probably is) veeeery slow. You should use /dev/zero instead.

syg00 · 05-18-2014, 09:13 PM

In the normal course of events, you'd hope that this was being done from a liveCD. /dev/sda is usually the boot device.
I have done this on laptops going back to leasing companies though.
Note this

Quote:

open("/dev/sda", O_WRONLY|O_CREAT|O_TRUNC, 0666to ) = -1 EACCES (Permission denied)

- that would have generated some output to the screen; the messages can be seen in the writes below. If you really, really want to do this to the entire disk, you must be root (or use sudo or such).

And yes, it's slow. A better option to check progress is to pass USR1 signal as the manpage suggests - that way you can get stats anytime, and (maybe) make an estimate of when it might be finished.

replica9000 · 05-18-2014, 11:39 PM

This will give you a progress bar. See man pv for more info

Code:

pv -pbert -s 60G < /dev/urandom > /dev/sda2

or

Code:

cat /dev/urandom | pv -pbert -s 60G | dd of=/dev/sda2 bs=1M

jrojsh · 05-19-2014, 12:32 PM

Quote:

In the normal course of events, you'd hope that this was being done from a liveCD. /dev/sda is usually the boot device.
I have done this on laptops going back to leasing companies though.

im a noob but yes, im on live usb... when i updated the os from mint 16 to 17, the mbr became corrupted somehow. it wouldnt load anything, would not give me grub access even. i could have just dd the boot sector but im thinking about ugrading the hdd and giving this away... so i thought id give dd a try and kill 2 birds with one stone.

Quote:

This will give you a progress bar. See man pv for more info

exactly what i needed. sitting here not knowing what if anything was happening was frustrating at best!

Quote:

/dev/urandom can be (and probably is) veeeery slow. You should use /dev/zero instead.

urandom is slow but i thought it was more secure, am i wrong or is zero better?

jpollard · 05-19-2014, 02:38 PM

Depends on how paranoid you are.

Using /dev/zero is sufficient for 99% of things - and it runs at the speed of the disk (might take 15-20 minutes for 60G, but could be less).