Essential Linux Commands and Quota Management

Here's a list of essential Linux commands:

• lime - Displays the current calendar.
• lime 1980 - Shows the calendar for the year 1980.
• cal 12 1980 - Displays the calendar for December 1980.
• date - Displays the current date.
• date -s "2009-11-05 18:55" - Changes the system time.
• who - Shows who is currently logged into the system.
• who -u - Displays the process ID (PID) of logged-in users.
• kill -9 3525 - Terminates the process with PID 3525.
• uname - Outputs the machine's name.
• uname -a - Shows detailed information about the machine.
• uptime - Displays how long the machine has been running.
• du - Displays disk space usage by folders.
• du -k - Displays disk space usage in 1024-byte blocks.
• df - Displays disk usage statistics.
• ps - Displays a general list of running processes.
• top - Displays a real-time view of the most resource-intensive processes.
• free - Shows memory availability and statistics.
• dmesg - Displays kernel messages.
• lsmod - Shows loaded kernel modules.
• lspci - Displays hardware components.
• man - Accesses the system's manual pages.
• whatis who - Shows a brief description of the who command.
• whereis who - Shows the location of the who command.

Vi Editor Tips:

• To quit and save changes: press Esc, then type :x and press Enter.
• To quit without saving changes: press Esc, then type :q! and press Enter.

Partitioning and Formatting

• fdisk -l - Lists existing partitions.
• mkfs.ext3 "path" - Formats a partition with the ext3 filesystem.
• fdisk /dev/hda - Opens the fdisk utility to create partitions on /dev/hda.

Partitioning Steps:

1. Press n for new partition.
2. Choose the partition type (primary or extended).
3. Specify the partition size (e.g., +1000M for 1000MB).
4. Press w to write the changes to disk.

After partitioning:

• partprobe - Informs the kernel about partition table changes.

Disk Quota Management

First, create users for comparison. It is assumed that you know how to create users.

To configure disk quotas:

1. Mount to view the Linux File System.
2. Edit /etc/fstab using nano.
3. Add the following lines (adjusting the path as needed):
   • LABEL=/home /home ext3 defaults 1 2
   • LABEL=/home /home ext3 defaults,usrquota,grpquota 1 2
4. Remount the filesystem: mount -o remount /home
5. Run quotacheck -augmv to create, verify, or repair quota control files. Alternatively, use quotacheck ugmv /home.
6. Verify that the home file system supports quotas by checking for aquota.user and aquota.group files in the /home directory: cd /home followed by ls -l.
7. Activate quota support: quotaon -ugv /home
8. To disable disk quotas: quotaoff -v /home

Now that the /home file system has quota support enabled, you can apply quotas to users and groups.

• edquota -u user1 - Grant quotas to user1.
• quota -u user1 - Check the quota settings for user1.
• quota -s -u user1 - View a report of quota usage for user1.
• edquota -t - Set the grace period (the time a user is allowed to exceed their quota) at the system level.
• edquota -u user1 -T - Set the grace period for user1.

To schedule quota warnings, edit /etc/crontab and add a line like:

0 0,12 * * * root /usr/sbin/warnquota

Other useful quota commands:

• quotacheck: To check the file system and update the quota system explicitly.
• repquota -a: Show details of shares in a particular file system.
• quotaon / quotaoff: To enable/disable quota system in a given file system.