Frandom - ArchWiki

# Frandom

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Reason: Needs updating to systemd. (Discuss in Talk:Frandom#)

frandom is a fast alternative to /dev/urandom.

From the frandom page: "The frandom suite comes as a Linux kernel module for several kernels, or a kernel patch for 2.4.22. It implements a random number generator, which is 10-50 times faster than what you get from Linux' built-in `/dev/urandom`."

Does frandom generate good random numbers? For anything not related to cryptography the answer is probably "yes". Don't use frandom for cryptographic purposes though, as it internally uses the dated and vulnerable RC4 algorithm.

Beneath in the example section, you'll find 'real', 'user' and 'sys' information, what they mean you can find here.

## Installation

Frandom is available as a package from the AUR[dead link 2020-03-29 ⓘ].

After installing frandom, you can make it available with:

    # modprobe frandom

The `/dev/frandom` device should now exist on the filesystem.

## Wiping a disk

Warning: frandom uses the vulnerable RC4 algorithm. Therefore:

- Do not use frandom for cryptographic purposes!
- Usage for "randomising" large hard drives prior to data-at-rest encryption is not recommended as `RC4` may be distinguished from random noise. See Securely wipe disk#Overwrite the target for other methods.

To use frandom to wipe a disk without encrypting it afterwards (for example for the simple destruction of data (even though overwriting the disk with /dev/zero would be sufficient and faster in this case)), use the dd command:

    # dd if=/dev/frandom of=/dev/sdX

Here, `X` refers to the drive you want to wipe.

Refer to Securely wipe disk for more general information on this topic.

## Example

1) On a 1.73 GHZ Thinkpad T43 with 2 GB ram:

    # time dd if=/dev/frandom of=/dev/sdb2
     dd: writing to `/dev/sdb2': No space left on device
     587384596+0 records in
     587384595+0 records out
     300740912640 bytes (301 GB) copied, 12844.6 s, 23.4 MB/s
     real    214m4.620s
     user    3m34.693s
     sys     77m28.660s

Summary: 300 GB in approx 3.5 hours

2) On a 2.4 GHZ (T8300 Core 2 Duo) Thinkpad T61 with 2 GB ram:

    # dd if=/dev/frandom of=/dev/sdb bs=1M
      dd: writing `/dev/sdb': No space left on device
      476941+0 records in
      476940+0 records out
      500107862016 bytes (500 GB) copied, 5954.52 s, 84.0 MB/s

Summary: 500 GB in approx 1.65 hours

3) On a 2.8 GHz (Athlon2 X4) with 4 GB ram:

    # dd if=/dev/frandom of=/dev/sdc3 bs=1M seek=100KB
      dd: writing `/dev/sdc3': No space left on device
      1807429+0 records in
      1807428+0 records out
      1895225712640 bytes (1.9 TB) copied, 20300.3 s, 93.4 MB/s

Summary: ~2TB in ~5.64 hours. However, on the same machine:

    # dd if=/dev/frandom of=/dev/null bs=1M count=1000
      1000+0 records in
      1000+0 records out
      1048576000 bytes (1.0 GB) copied, 7.81581 s, 134 MB/s

versus

    # dd if=/dev/urandom of=/dev/null bs=1M count=1000
      1000+0 records in
      1000+0 records out
      1048576000 bytes (1.0 GB) copied, 144.296 s, 7.3 MB/s

This makes frandom 10-20 times faster on this machine, meaning it would take approx 50-120 hours (2-5 days!) to randomize 2TB using urandom.

4) On a 2.70GHz (i7-2620M) ThinkPad x220 with 8GB Ram:

    # time dd if=/dev/frandom of=/dev/sdc
      dd: writing to `/dev/sdc': No space left on device
      625140336+0 records in
      625140335+0 records out
      320071851520 bytes (320 GB) copied, 9618.12 s, 33.3 MB/s
      real    160m18.126s
      user    1m8.916s
      sys     36m16.401s

Summary: 320 GB in approx. 2.67 hours

5) On a 2.70GHz (i7-2620M) ThinkPad x220 with 8GB Ram:

    # time dd if=/dev/frandom of=/dev/sdc
      dd: writing to `/dev/sde': Input/output error
      467085833+0 records in
      467085832+0 records out
      239147945984 bytes (239 GB) copied, 24675.2 s, 9.7 MB/s
      real    411m15.208s
      user    2m58.028s
      sys     83m14.188s

Summary: 500 GB in approx. 6.85 hours (connected on USB3)

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