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Top Forums UNIX for Advanced & Expert Users Cmd 'cat /dev/urandom' not closing cleanly Post 302994400 by user052009 on Wednesday 22nd of March 2017 12:41:58 PM
Old 03-22-2017
Cmd 'cat /dev/urandom' not closing cleanly

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.

Code:
PASSWORD="$(cat /dev/urandom | tr -dc "a-zA-Z0-9" | fold -w 16 | head -1)Aa0!"

The code worked as expected but the side effects were definitely unexpected. Any idea how I can enhance this to ensure the urandom stream gets closed after it's been called and therefore prevent the server from becoming overloaded?
Many thanks.
 

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RANDOM(4)						   BSD Kernel Interfaces Manual 						 RANDOM(4)

NAME
random , urandom -- random data source devices. SYNOPSIS
pseudo-device random DESCRIPTION
The random device produces uniformly distributed random byte values of potentially high quality. To obtain random bytes, open /dev/random for reading and read from it. The same random data is also available from getentropy(2). Using the getentropy(2) system call interface will provide resiliency to file descriptor exhaustion, chroot, or sandboxing which can make /dev/random unavailable. Additionally, the arc4random(3) API provides a fast userspace random number generator built on the random data source and is preferred over directly accessing the system's random device. /dev/urandom is a compatibility nod to Linux. On Linux, /dev/urandom will produce lower quality output if the entropy pool drains, while /dev/random will prefer to block and wait for additional entropy to be collected. With Yarrow, this choice and distinction is not necessary, and the two devices behave identically. You may use either. The random device implements the Yarrow pseudo random number generator algorithm and maintains its entropy pool. The kernel automatically seeds the algorithm with additional entropy during normal execution. FILES
/dev/random /dev/urandom HISTORY
A random device appeared in the Linux operating system. Darwin September 6, 2001 Darwin
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