In Linux, all the devices are treated as files that are stored in /dev directory.
IDE disks are saved as /dev/hd[a-d]
SCSI/SATA/USB disks are saved as /dev/sd[a-p]
USB devices are saved as /dev/sd[a-p] (same as SATA disks)
Partition Table lies on the first sector of a disk. The size of the Partition Table is 64 bytes and it can only contain 4 partition records that are either primary partition or extended partition.
For example, if a disk is named /dev/sdb and is divided into 4 partitions, P1-P4. They are named as,
In fact, extended partition can be divided into more partitions called logical partition. Thanks to this technology, we can create more than 4 partitions on a disk.
Master Boot Record
Master Boot Record (MBR) is located on the first sector of a disk. It records the boot information of the disk. The boot loader is stored in MBR. MBR is 446 bytes.
BIOS->MBR->Boot Loader (stored in MBR)->Kernel
command format — command [-options] parameter1 parameter2
1. In Linux, all commands and filenames are capital sensitive. ‘cd’ and ‘CD’ represent completely different things.
2. Slash ‘\’ at the end of a line represents current command is not finished and would be continued in the next line.
Mount/umount – mount/unmount a partition to a specified directory
Mount a partition means to utilize a directory as the entry to the partition, and put all the data in the partition under the directory. Linux uses directory tree structure to organize files.
If I insert a CD in my computer,
in Windows, it would appear as a new driver in “my computer”, say E:\
in Linux, it would appear as a new directory under the root directory “/media/cdrom/”. It can also be mounted to any other directories, say /mnt/cdrom
1. umount the first partition of first disk (/dev/sda1) which is usually named C:\ in Windows.
2. create a directory /mnt/c
3. mount /dev/sda1 to /mnt/c direcotry
4. list directories and files under the c
date – show date and time
cal – show calendar
bc – a simple calculator
man [command/filename] — show the manual page of some commands or files
‘/[word]’ search the [word] in man page.
‘n’ and ‘N’ next match / previous match.
man -f [name] find a command whose name contains the key word. It is the same as ‘whatis’
man -k [description] find a command whose description contains the key word. It is the same as ‘apropos’
The meaning of the code at the top-left of each man page: (LS(1)) in this example
1 — commands or executable files that can be run in shell by users.
2 — functions or tools that is callable by kernel.
3 — some common functions and libraries, mostly belongs to C lib.
4 — descriptions of device files under /dev
5 — configuration file or the format of some files
6 — games
7 — protocols, such as Linux file system, network protocol, ASCII code, etc.
8 — administrative commands accessible to system administrator.
9 — kernel related file
info — similar to man
In face, both info and man opens a file describing the specified command or file. The file is located at /usr/share/man or /usr/share/info.
Other manual documents for installed packages are stored in /usr/share/doc
Function of some system directories
~ home directory of current user. For root user, ~ means /boot. For other user, ~ means /home/[username]
/boot/ – stores boot related files.
Tip: Some out-of-date BIOSs may not recognize large disks. So it’s important to divide a small partition (100MB) at the beginning of your disk to store the files under /boot for the sake of a successful booting.
/etc/passwd – Users’ information
/etc/shadow – User’s password
/etc/group – Group names
[Tab] Make up unfinished part of command.
[Ctrl] + D Means End of File (EOF) or typing ‘exit’ in the terminal. Exit the current process.
[Ctrl] + C Send a sigint signal to current running process. End and exit the current process.