You are managing an FTP server installed in Ubuntu Server. The server has created a very large log le, vsftpd.log. Which command is appropriate to search the log le for activity of the user charlie?
a. sudo cat /var/log/vsftpd.log
b. grep "charlie" /var/log/vsftpd.log
c. sudo grep "charlie" /var/log/vsftpd.log
d. cat /var/log/vsftpd.log