HDD and partitions

df -h - How much free disk space is available for each mount.

mount -t auto /dev/cdrom /cdfolder - mounts cdrom to /cdfolder
umount /cdfolder - unmounts cdfolder

fdisk -l - show hard drives and partitions
fdisk /dev/sda - start fdisk for sda hard drive
commands:
a - bootable flag
p - display partitions table
d - delete a partition
n - create a new partition
t - change partition's ID (83 - for ext2)
q - exit without saving changes
w - save changes and exit

mkfs -t ext2 /dev/sdb1 - build an ext2 file system in an empty partition
fsck -f -y /dev/sdb1 - check and repair a file system on sdb1

Mount hdc1 partition to a /data folder automatically on boot

1. Open /etc/fstab
2. Add line:    /dev/hdc1                 /data                   ext2                defaults             1 2
3. Restart computer

badblocks -n -s -v /dev/hda - Check hda disk for bad blocks.
-n - Use non-destructive read-write mode (only if disk is not mounted). Default - non-destructive read-only test.
-s - Show progress
-v - Verbose mode

File and Folder manipulations

ls -l --block-size=1M - list files in current directory with sizes in MB (K for KB)
ls *.img | wc - count .img files current directory

cp -r /source/directory /target/directory - Copy existing folder to new location

rm -r /dirctory - Remove a directory with contents
rm * - remove all files from directory

mv old-name new-name - rename files and folders

find -name "example*" - Search for files and folders beginning "example". Searches in in the current directory and subdirectories.
find / -name "example*" - The same as above but searches in root and all subdirectories.
find -name '*' -size +500M - Search for all files larger than 500MB.

du --max-depth=1 -h - List of folders with their sizes in current directory.
du -all --max-depth=1 -h - As above, but also include files.

tar -zcvf htdocs.tar.gz htdocs - compress htdocs directory
tar -zxvf htdocs.tar.gz - extract htdocs.tar.gz file
-z Compress using gzip
-c Create archive
-v Verbose
-f Archive File name
-x Extract files

Other

ifconfig - TCP/IP network interface parameters.

su - Become super user or another user.
sudo - Execute a command as the superuser or other user.

chmod -R 777 /folder - set 777 (full) permissions for folders

Startup scripts can be placed in rc.local
it could be in /etc or /etc/rc.d

apt-get install build-essential - installs all common compilers at once

tail -f /var/log/file.log - Monitors a log file in a real time. All new added lines will be outputted on a display. To interrupt press CTRL + C