Sha256 checksum on terminal displaying strange characters

I've installed the hashalot first to use the sha256.
Then something strange happened when using the command + filename:

mlockall: Cannot allocate memory
Warning: couldn't lock memory, are you root?
Enter passphrase:

I've never needed to enter passphrase before for this as far as I remember. And if I do provide a password or use sudo before running the command I get strange characters on result:

��z�9��E-�c���F�K��"�x~�(8�J��

I am on an OS based on Ubuntu (Elementary OS Freya).

Solution 1:

Did you read the description of the package you installed?

This program will read a passphrase from standard input and print a binary (not printable) hash to standard output.

You tried to print the output to console; what you're seeing is expected behavior.

Solution 2:

ubuntu 16.04 default max shared memory per user is 64k. I upped it to 1gb for all users, error goes away.

by adding a line to the end of the /etc/security/limits.conf file will fix this. no need to reboot the system, you'll need to logout though.

$ echo test  | sha256 -s test | base64
mlockall: Cannot allocate memory
Warning: couldn't lock memory, are you root?
NyaDNd1pMQRb3N+SYj/4GaZCRLU9DnRtQ4eXNJ1NpXg=

$ ulimit -l
64
$ sudo bash
# echo "*   -     memlock   1048576" >> /etc/security/limits.conf

log out now.

$ ulimit -l
1048576

$ echo test  | sha256 -s test | base64
NyaDNd1pMQRb3N+SYj/4GaZCRLU9DnRtQ4eXNJ1NpXg=

no more tears!!

I'm guessing this warning is about the corner case of having your secrets paged out of memory, and someone finding it latter in tmp space.