10 More Discussions You Might Find Interesting
1. HP-UX
Hi,
In our HP-UX B.11.11. I could not find dev/urandom and dev/random
Are all pseudo-devices implemented as device drivers, or in need to run /configure some package to install the package to have dev/urandom.
Please help (4 Replies)
Discussion started by: rashi
4 Replies
2. UNIX for Advanced & Expert Users
Hi
I'm running the following command to generate a random password in a KSH script on a RHEL Linux VM but for some reason the cmd is not being closed and it's causing problems on the host.
PASSWORD="$(cat /dev/urandom | tr -dc "a-zA-Z0-9" | fold -w 16 | head -1)Aa0!"
The code worked as... (2 Replies)
Discussion started by: user052009
2 Replies
3. Shell Programming and Scripting
Hello,
I'm trying to send the error output of a 'cat' operation to /dev/null like this:
cat /dirA/dirB/temp*.log > /dirA/dirB/final.log 2>/dev/null
This works perfectly in a terminal, but not when placed in a script.
If there are no files matching temp*.log the script outputs an error... (7 Replies)
Discussion started by: Nils88
7 Replies
4. Slackware
I am having problems using soundes. Until a few moments ago
the following commands produced errors and no sound:
cat /usr/share/apps/kolf/sounds/blackhole.wav/ > /dev/dsp yielded:
/dev/dsp: Invalid argument
cat /usr/share/apps/kolf/sounds/blackhole.wav > /dev/audio yelded:
/dev/audio:... (3 Replies)
Discussion started by: slak0
3 Replies
5. Shell Programming and Scripting
I have a file with a single filename in it, which I want to assign to a BASH variable, so I've been trying:
c=$(head -1 somefile)
echo $c
which outputs correctly, but them when I do
...
somecommand $c
it says it can't find the file, is that because it's grabbing the whole line, and... (5 Replies)
Discussion started by: unclecameron
5 Replies
6. Shell Programming and Scripting
cat myname.txt
John Doe I
John Doe II
John Doe III
-----------------------------------------------------------------------
for i in `cat myname.txt`
do
echo This is my name: $i >> thi.is.my.name.txt
done
-----------------------------------------------------------------------
cat... (1 Reply)
Discussion started by: danimad
1 Replies
7. UNIX for Dummies Questions & Answers
Hi,
Excuse my ignorance here - I'm a networks man and my knowledge of all things unix is somewhat limited.
We have a very large file (/var/tmp/mond.log) that we need to zero - does the "cat /dev/null > /var/tmp/mond.log" command achieve this? (4 Replies)
Discussion started by: freakydancer
4 Replies
8. UNIX for Dummies Questions & Answers
Hi, how do I use /dev/urandom to generate a single number between 1-100? I can od /dev/urandom but it gives me an endless list of random numbers, I just want 1 between 1-100. How can I get that? Thanks. (12 Replies)
Discussion started by: Takumi
12 Replies
9. UNIX for Dummies Questions & Answers
I've a major file which includes other files and now I wanna 'cut' the file in several minor parts....like
....
find / -name "*.tmp" >filea
wc -l filea >fileb
sed -e '1s/ filea//' fileb >filec
AMOUNT=`cat filec`
if ; then
cat file a |head -100l (ell) |tail -100l >filec
cat file a |head... (6 Replies)
Discussion started by: svennie
6 Replies
10. Shell Programming and Scripting
hai
in my shell script i want to replace the following commands
1) more
2) head
3) tail
i want to try all type of possible options avaliabul in the above commands
please help in implementing those commands (9 Replies)
Discussion started by: g_s_r_c
9 Replies
RANDOM(4) Linux Programmer's Manual RANDOM(4)
NAME
random, urandom - kernel random number source devices
DESCRIPTION
The character special files /dev/random and /dev/urandom (present since Linux 1.3.30) provide an interface to the kernel's random number
generator. File /dev/random has major device number 1 and minor device number 8. File /dev/urandom has major device number 1 and minor
device number 9.
The random number generator gathers environmental noise from device drivers and other sources into an entropy pool. The generator also
keeps an estimate of the number of bit of the noise in the entropy pool. From this entropy pool random numbers are created.
When read, the /dev/random device will only return random bytes within the estimated number of bits of noise in the entropy pool.
/dev/random should be suitable for uses that need very high quality randomness such as one-time pad or key generation. When the entropy
pool is empty, reads to /dev/random will block until additional environmental noise is gathered.
When read, /dev/urandom device will return as many bytes as are requested. As a result, if there is not sufficient entropy in the entropy
pool, the returned values are theoretically vulnerable to a cryptographic attack on the algorithms used by the driver. Knowledge of how to
do this is not available in the current non-classified literature, but it is theoretically possible that such an attack may exist. If this
is a concern in your application, use /dev/random instead.
CONFIGURING
If your system does not have /dev/random and /dev/urandom created already, they can be created with the following commands:
mknod -m 644 /dev/random c 1 8
mknod -m 644 /dev/urandom c 1 9
chown root:root /dev/random /dev/urandom
When a Linux system starts up without much operator interaction, the entropy pool may be in a fairly predictable state. This reduces the
actual amount of noise in the entropy pool below the estimate. In order to counteract this effect, it helps to carry entropy pool informa-
tion across shut-downs and start-ups. To do this, add the following lines to an appropriate script which is run during the Linux system
start-up sequence:
echo "Initializing kernel random number generator..."
# Initialize kernel random number generator with random seed
# from last shut-down (or start-up) to this start-up. Load and
# then save 512 bytes, which is the size of the entropy pool.
if [ -f /var/random-seed ]; then
cat /var/random-seed >/dev/urandom
fi
dd if=/dev/urandom of=/var/random-seed count=1
Also, add the following lines in an appropriate script which is run during the Linux system shutdown:
# Carry a random seed from shut-down to start-up for the random
# number generator. Save 512 bytes, which is the size of the
# random number generator's entropy pool.
echo "Saving random seed..."
dd if=/dev/urandom of=/var/random-seed count=1
FILES
/dev/random
/dev/urandom
AUTHOR
The kernel's random number generator was written by Theodore Ts'o (tytso@athena.mit.edu).
SEE ALSO
mknod (1)
RFC 1750, "Randomness Recommendations for Security"
Linux 1997-08-01 RANDOM(4)