As a regular user, you can use the following command to search the /etc directory for every file named passwd and redirect error messages to /dev/null:

find /etc -name passwd 2>/dev/null

You can find files under the /usr/share/doc directory that have not been modified in more than 300 days using the following command:

find /usr/share/doc -type f -mtime +300

To find all files on your system which are longer than 1 MiB and output their names, you can use the following command:

find / -size +1M -type f -exec ls -lh {} \;

To delete a file with an unusual name using find, you can use the following command:

find . -type f -name 'file_with_unusual_name*' -exec rm {} \;

To ensure that files in /tmp which belong to you are deleted once you log out, you can use a tool like tmpwatch to clean up files older than a certain time. You can add a cron job to run tmpwatch at regular intervals.

To find all files on your system called README, you can use the following command:

find / -name README -type f