All Questions(ubuntu)

While using nohup to put a command to run in background some of content appear in terminal.

cp: error reading ‘/mnt/tt/file.txt’: Input/output error
cp: failed to extend ‘/mnt/tt/file.txt’: Input/output error

I want to save that content to a file.

I read that terminal is nothing but shell, and Unix provides different flavors of shells:

• Bourne shell (sh)
• C shell (csh)
• TC shell (tcsh)
• Korn shell (ksh)
• Bourne Again shell (bash)

Questions:

• When I open a terminal window, which shell is opened by default?
• How do I check how many shells are installed?
• How do I change the shell used from my account?

I would like to write a bash script to decode a base64 string. For example I type decode QWxhZGRpbjpvcGVuIHNlc2FtZQ== and it prints Aladdin:open sesame and returns to the prompt.

So far I have tried a simple bash file containing python -m base64 -d $1 but this command expects a filename not a string. Is there another non-interactive command (not necessarily in a Python module) that I can run from the command line to achieve this, without having to install any extra packages? (Or if I do, something super-minimal.)

I am installing p4v in /opt, but /usr/bin is on my path. Is it possible to create a soft or symbolic link for p4v from /opt to /usr/bin, so I can just type "p4v" since /usr/bin is in my path?

Often, crontab scripts are not executed on schedule or as expected. There are numerous reasons for that:

1. wrong crontab notation
2. permissions problem
3. environment variables

This community wiki aims to aggregate the top reasons for crontab scripts not being executed as expected. Write each reason in a separate answer.

Please include one reason per answer - details about why it's not executed - and fix(es) for that one reason.

Please write only cron-specific issues, e.g. commands that execute as expected from the shell but execute erroneously by cron.