To change the OpenSSH port number on CentOS Linux 5/6, you need to edit the sshd_config file. Here’s how: Open the sshd_config file: sudo nano /etc/ssh/sshd_config Locate the line that starts with Port: Port 22 Change the port number to the desired value (e.g., 2222): Port 2222 Save the changes and close the file. Restart … Read more

In CentOS/RHEL, you can use the yum versionlock plugin to lock a package version at a particular version. This will prevent the package from being upgraded, even if a newer version is available in the repository. Here’s how you can lock a package version: Install the yum-versionlock plugin: yum install yum-plugin-versionlock Find the package and … Read more

In Linux/Unix, you can use the last command to check the last time a user logged in on the system. By default, the last command shows the list of all users who have logged in to the system, with the most recent login listed first. To see the last time a specific user logged in, … Read more

To check for new files in the /var/www/uploads/ directory in Unix/Linux, you can use the following command: ls -ltr /var/www/uploads/ | tail The ls -ltr command lists the contents of the directory in long format and sorts the output by modification time (-t) in reverse (-r) order. The tail command at the end shows the … Read more

To prevent yum from upgrading the Linux kernel on a CentOS/Red Hat Enterprise Linux system, you can use the following method: Create a file in the /etc/yum.conf.d/ directory with a descriptive name, such as kernel-updates.conf. Add the following lines to the file: exclude=kernel* Save the file and close it. This will exclude the kernel packages … Read more

The noexec, nosuid, and nodev mount options can be used to increase the security of NFS client mount points. These options control the execution of executable files, set-user-id (SUID) files, and device files, respectively. Here is how you can mount an NFS share with these options on a web server: Create a directory to mount … Read more

To log suspicious Martian packets (packets with un-routable source addresses) in Linux, you can modify the kernel’s syslog configuration. Here is an example of how to do it: Edit the /etc/sysctl.conf file and add the following line: net.ipv4.conf.all.log_martians = 1 Save the changes and reload the sysctl configuration: sysctl -p Configure the syslog daemon to … Read more

In Ubuntu, the cp command is used to copy files and directories. Here’s the basic syntax of the cp command: cp [OPTION]… SOURCE DEST Where SOURCE is the file or directory that you want to copy, and DEST is the destination directory where you want to copy the file to. For example, to copy a … Read more

In the cp or mv commands in bash shell, {,} is used to specify multiple target destinations for the source file(s). It’s a brace expansion feature in bash, which allows you to repeat a command multiple times with different arguments. For example, if you want to copy a file “file1.txt” to two different directories, you … Read more

To show disk quota limits on a FreeBSD system, you can use the quota command. This command displays the disk usage and limits for users and groups. For example, to display the disk quotas for a specific user, run the following command: quota username To display the disk quotas for all users on the system, … Read more