Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
Perform AES256 encryption on a string using command
Answer:
To encrypt a string using AES256, you can use the openssl tool.
# echo -n 'apple' | openssl enc -aes256 -k password -nosalt -iv 0 -a -p
key=1F3870BE274F6C49B3E31A0C6728957F0628DEF3179C824405825F85F5527096
iv =00000000000000000000000000000000
PMcE/8RE+RLRlQWT5tlLWA==
Check for the number of connection from a particular IP address
Answer:
You can check the total number of connections from a particular IP address:
# netstat -ntu | awk '{print $5}'| cut -d: -f1 | sort | uniq -c | sort -nr | more
It will give something like:
25 192.168.1.2
13 192.168.1.3
..
Simple file encryption with OpenSSL
Answer:
You have a single file (input.txt), and you want to encrypt it with a password, it is easy with OpenSSL.
# openssl aes-128-cbc -salt -in input.txt-out input.aes
Enter the password twice.
When you want to decrypt it, use the command.
# openssl aes-128-cbc -d -salt -in input.aes -out output.txt
Add a user that can gain root privileges in Ubuntu
Answer:
You have created a user, and now you want to make this user (e.g. peter as an example) can gain root privileges.
Firstly, check your /etc/sudoers file
# sudo cat /etc/sudoers
You might found the following lines
# Members of the admin group may gain root privileges
%admin ALL=(ALL) ALL
john ALL=(ALL) ALLMethod 1
If you have the line %admin ALL=(ALL) ALL, then you can add the user (e.g peter) to the admin group using the command:
# sudo usermod -g admin peter
Method 2
Or you can edit the file /etc/sudoers to add your account manually
# sudo visudo
Append peter ALL=(ALL) ALL at the end..
%admin ALL=(ALL) ALL
john ALL=(ALL) ALL
peter ALL=(ALL) ALLHow to check failed login attempt in Ubuntu
Answer:
Every login attempts are logged in the file /var/log/auth.log in Ubuntu.
To check failed login attempt(s),
E.g.
# grep 'Failed password' /var/log/auth.log
Jan 31 14:00:27 localhost sshd[16141]: Failed password...
Jan 31 14:00:46 localhost sshd[16141]: Failed password...
Jan 31 14:00:49 localhost sshd[16141]: Failed password...
