If a linux system user is able to login on the shell or with SSH depends on its shell setting in /etc/passwd. If you want to prevent that a certain user is able to login, then set the shell either to /bin/false or /sbin/nologin.

Example for Debian and Ubuntu Linux for the user with the username “otheruser”:

usermod -s /bin/false otheruser

For Redhat, Fedora or CentOS use /sbin/nologin:

usermod -s /sbin/nologin otheruser

Warning: Do not set the shell for the root user to /bin/false or /sbin/nologin!

There is no simple tolower command on the bash, but with a little shell script you can convert uppercase characters to lowercase. The script uses the tr command internally for converting the chars.

Create a shell script with the name tolower:

vi /usr/local/bin/tolower

and enter the following content:

#!/bin/sh
echo $1 | tr '[:upper:]' '[:lower:]'

Then make the script executable:
<p class="command">chmod +x /usr/local/bin/tolower

An test it by executing this command on the shell:

tolower "Thats a Test"

will convert the string to lowercase and show the result on the shell:

thats a test

One way to create a backup of a mysql database on the shell is to use the mysqldump command. Mysqldump creates a dump of the database in form of sql commands.

Backup

mysqldump -u root -p mydatabase > /tmp/backup_mydatabase.sql

This command creates a backup of the database with the name “mydatabase” in the file /tmp/backup_mydatabase.sql

Restore

To restore the backup, use the command:

mysql -u root -p mydatabase < /tmp/backup_mydatabase.sql

To turn on verbose logging (e.g. to debug FTP connection or authentication problems) in  pure-ftpd FTP server on Debian and Ubuntu Linux, execute the following command as root user in the shell:

echo 'yes' > /etc/pure-ftpd/conf/VerboseLog

and then restart pure-ftpd

/etc/init.d/pure-ftpd-mysql restart

The debug output will be logged to syslog. To view the log content, execute:

tail -n 100 /var/log/syslog

To disable verbose logging, execute these commands:

rm -f /etc/pure-ftpd/conf/VerboseLog
/etc/init.d/pure-ftpd-mysql restart