Linux Basics

1. Introduction

Most users are accustomed to the graphical interface of Windows. While the Omni3576’s basic daily applications can be managed through its graphical interface, certain operations—such as system configurations—must be performed outside of it. However, almost all programs can be run through the command line. Mastering commonly used Linux commands is therefore crucial for beginners. This chapter introduces frequently used Linux commands to enhance the experience of developing on the Omni3576.

2. Terminal Overview

On the Omni3576, you can access the terminal through a serial port or via SSH. For local display logins, press Ctrl+Alt+T to open the default terminal. The Omni3576's default terminal prompt looks like this:
```
luckfox@luckfox:~$ 
```
- luckfox: Current username or login name.
- luckfox: Hostname.
- ~: Indicates the current directory is /home/luckfox.
- $: Denotes a normal user login.
- #: Denotes a root user login

Omni3576默认登录普通 luckfox 用户，想要切换 root 用户，在终端输入：

sudo su root   # Switch from a regular user to the root user.
su luckfox     # Switch from the root user to a regular user.

3. Linux File Structure

In Windows, each partition is an independent tree structure, with one tree per partition. In Linux, however, there is only one tree structure, with all files and partitions existing under a single hierarchy. The root directory is at the top, and all other directories, files, and partitions are created beneath it. Common directories include:

/bin: Contains binary executable files related to the Omni3576 system (including those needed for running the graphical interface).
/boot: Stores the Linux kernel and other packages required to boot the Omni3576.
/dev: Device directory; in Linux, all devices are treated as files. This directory contains device files, such as sda for the first SATA hard drive or USB stick.
/etc: System management and configuration files.
/home: User directories; data for all users (except the root user) are stored here.
/lib: Stores dynamic link libraries for the basic system.
/media: Contains mount points for removable drives like USB sticks and optical drives.
/root: The home directory for the system administrator (also known as the superuser).

4. File System

In Linux, all resources managed by the operating system—such as network cards, disk drives, printers, input/output devices, regular files, or directories—are treated as files. This concept, "everything is a file," is fundamental to Linux. The File System is a mechanism used by the operating system to manage and organize data on storage devices (like hard drives, SSDs, and flash memory). It defines how files are stored, retrieved, and managed. Common Linux file systems include:

EXT2: An early Linux file system without journaling, suitable for small storage devices like USB drives.
EXT3: An upgraded version of EXT2 with journaling, significantly improving data security and file recovery.
EXT4: The most widely used Linux file system, supporting large files (up to 16 TB) and robust performance, stability, and security.
XFS: A high-performance 64-bit journaling file system designed for large files and high-concurrency applications.
JFFS2 and UBIFS: File systems designed for flash storage. They feature wear leveling and power failure protection, reducing storage wear.

4.1 inode and block Overview

inode is a metadata structure in the Linux file system that records a file's attributes (e.g., size, permissions, timestamps) but does not store the file name or data. Each file or directory is assigned a unique inode when created. Data is stored in blocks (the smallest unit of storage on a disk), which typically have a size of 4 KB.

To check sector size:

root@luckfox:/home/luckfox# fdisk -l /dev/mmcblk1
Disk /dev/mmcblk1: 29.13 GiB, 31272730624 bytes, 61079552 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 46680000-0000-454D-8000-121D00005F9A

Device          Start      End  Sectors  Size Type
/dev/mmcblk1p1  16384    24575     8192    4M unknown
/dev/mmcblk1p2  24576    32767     8192    4M unknown
/dev/mmcblk1p3  32768   163839   131072   64M unknown
/dev/mmcblk1p4 163840   425983   262144  128M unknown
/dev/mmcblk1p5 425984   491519    65536   32M unknown
/dev/mmcblk1p6 491520 61079518 60587999 28.9G unknown

root@luckfox:/home/luckfox# cat /sys/block/mmcblk1/queue/hw_sector_size
512

To view inode information:

luckfox@luckfox:~$ tee 1.txt <<EOF
> 1111
> 1111
> 1111
> EOF

luckfox@luckfox:~$ stat 1.txt
  File: 1.txt
  Size: 15              Blocks: 8          IO Block: 4096   regular file
Device: 179,6   Inode: 95246       Links: 1
Access: (0644/-rw-r--r--)  Uid: ( 1000/ luckfox)   Gid: ( 1000/ luckfox)
Access: 2024-08-26 12:51:16.816002017 +0000
Modify: 2024-08-26 12:51:35.924002026 +0000
Change: 2024-08-26 12:51:35.924002026 +0000
 Birth: 2024-08-26 12:51:16.816002017 +0000

Access: (0644/-rw-r--r--): File permissions
Access: 2024-08-26 12:51:16.816002017 +00: Last access time of the file
Modify: 2024-08-26 12:51:35.924002026 +0000: Last modification time of the file content
Change: 2024-08-26 12:51:35.924002026 +0000: Last change time of the file's metadata (e.g., permissions or owner)
Birth: 2024-08-26 12:51:16.816002017 +0000: Creation time of the file (not supported by all file systems)

4.2 inode Considerations

The number of inodes is finite. If inodes are exhausted, new files or directories cannot be created, even if disk space is available.
Files with special characters in their names may be difficult to delete. Deleting such files by inode can resolve the issue:
```
find ./* -inum <inode-number> -delete
```

4.3 Symbolic Links vs. Hard Links

Feature	Hard Link	Symbolic Link
Reference Method	Points to the same inode	Points to a file path
Cross-File System Support	Not supported	Supported
Effect of Source Deletion	Link remains valid	Link becomes invalid
Creation Command	ln filename linkname	ln -s target linkname
Supported Targets	Any file	Any file or directory

5. Frequently Used Linux Commands

ls

Command Function

The ls command is used to display the contents of a specified working directory (i.e., list the files and subdirectories in the current working directory).

Command Format

ls [-ahl] directory]

Parameter Description

Parameter	Description	Path
directory	Target directory to display	Can be a relative or absolute path.

Usage Examples

ls -a  # Display all files and directories, including hidden files (starting with .)
ls -l  # List detailed information such as file type, permissions, owner, and size
ls -lh # Show file sizes in a human-readable format, e.g., 4K
ls -i  # Display inode numbers of files

cd

Command Function

The cd command is used to change the current working directory.

Command Format

cd [ directory ]

Parameter Description

Parameter	Description	Value
directory	Target directory to switch to. Can be a relative or absolute path.	A string without spaces; absolute path length is 1–64.

Usage Examples

cd          # Return to the user's home directory
cd ..       # Navigate to the parent directory
cd /bin     # Enter the /bin directory
cd ../..    # Move up two levels in the current directory
cd ~        # Enter the user's home directory
cd -        # Switch to the last visited directory

pwd

Command Function

The pwd command displays the working directory. Running this command shows the absolute path of the current working directory.

Usage Examples

# pwd
/bin           # Output

df

Command Function

The df command displays disk space usage statistics for the file systems in the Linux system.

Usage Examples

luckfox@luckfox:~$ df -Th
Filesystem     Type      Size  Used Avail Use% Mounted on
/dev/root      ext4       29G  3.7G   24G  14% /
devtmpfs       devtmpfs  1.9G  8.0K  1.9G   1% /dev
tmpfs          tmpfs     2.0G     0  2.0G   0% /dev/shm
tmpfs          tmpfs     781M  1.5M  779M   1% /run
tmpfs          tmpfs     5.0M  8.0K  5.0M   1% /run/lock
tmpfs          tmpfs     391M   32K  391M   1% /run/user/1000

touch

Command Function

The touch command modifies the timestamp attributes (access and modification times) of a file or directory. If the file does not exist, it creates a new file.

Usage Examples

touch file.txt       # Create a new file named "file.txt"

mkdir

Command Function

The mkdir command is used to create directories.

Command Format

mkdir [ options ] directory

Parameter Description

Parameter	Description
options	-p Create parent directories if they do not exist
directory	Name of the directory to create.

Usage Examples

mkdir luckfox              # Create a subdirectory named "luckfox"
mkdir -p luckfox/test      # Create a directory named "luckfox/test"

cp

Command Function

The cp command is mainly used to copy files or directories.

Command Format

cp [ options ] source dest

Parameter Description

Parameter	Description
options	Options like -r, -f, etc.
source	Path and name of the file to copy.
dest	Path and name of the destination.

Usage Examples

cp test.txt /bin           # Copy "test.txt" to the /bin directory
cp –r test/ /usr/newtest   # Copy "test" directory to /usr and rename it to "newtest"

mv

Command Function

The mv command is used to rename files or directories or move them to another location.

Command Format

mv [ options ] source dest

Parameter Description

Parameter	Description
options	Options like -i, -f, etc.
source	Path and name of the file to move.
dest	Path and name of the destination.

Usage Examples

mv file1 /userdata          # Move "file1" to the /userdata directory

rm

Command Function

The rm command is used to delete files or directories.

Command Format

rm [ options ] file/directory

Parameter Description

Parameter	Description
options	Options like -r, -f, etc.
file/directory	Name of the file or directory to delete.

Usage Examples

rm test.txt         # Delete the file "test.txt"
rm -r Luckfox       # Delete the directory "Luckfox"

chmod

Command Description

The chmod command is used to control file permissions for users in Linux.

Command Explanation

File permissions in Linux/Unix are divided into three levels: file owner (Owner), group (Group), and other users (Other Users).

In the terminal output below, the most important part is the first column, which describes file and directory permissions in detail. The third and fourth columns show the user or group that the file or directory belongs to.

# ls -lh
drwxr-xr-x    2 1002     1002         160 media
lrwxrwxrwx    1 1002     1002           3 lib64 -> lib
lrwxrwxrwx    1 1002     1002           3 lib32 -> lib
drwxrwxr-x    6 1002     1002         664 rockchip_test
drwxrwxr-x    5 1002     1002         576 userdata
lrwxrwxrwx    1 1002     1002          11 linuxrc -> bin/busybox
drwxr-xr-x    2 1002     1002         160 root
drwxrwxr-x    2 1002     1002        2.2K sbin
dr-xr-xr-x  114 root     root           0 proc
lrwxrwxrwx    1 1002     1002           8 data -> userdata
drwxrwxr-x    6 1002     1002         544 usr
drwxr-xr-x    4 1002     1002         672 var
dr-xr-xr-x   13 root     root           0 sys
drwxrwxrwt    2 root     root          60 tmp
drwxr-xr-x    3 root     root          80 run
drwxr-xr-x    2 1002     1002         160 opt
drwxrwxr-x    3 1002     1002         296 oem
drwxr-xr-x    3 1002     1002         224 mnt
drwxrwxr-x    3 1002     1002        2.0K lib
drwxrwxr-x    6 1002     1002        1.5K etc
drwxr-xr-x   12 root     root        1.9K dev
drwxrwxr-x    2 1002     1002        4.1K bin

File attributes in Linux can be divided into three types: read (r), write (w), and execute (x). However, the file attributes shown above are divided into 10 small cells because, apart from the first cell that indicates the directory, the other three groups of three cells each represent the file owner's permissions, the permissions of the same group, and the permissions for other users. In the first column, if it shows "d," it means it is a directory; if it is a symbolic link, it shows "l"; if it is a device file, it shows "c".
- The first "rwx" column: "- rwx --- ---" represents the permissions owned by the file owner.
- The second "rwx" column: "- --- rwx ---" represents the permissions of users in the same group.
- The third "rwx" column: "- --- --- rwx" represents the permissions of other users.
- "rwx rwx rwx" means that any user can read, write, and execute this file.
- "rw- --- ---" means that only the file owner has read and write permissions, but no execute permissions.
- "rw- rw- rw-" means that all users have read and write permissions.

Symbolic Mode

who (user type)
who User Type Description
u user File owner
g group Users in the same group
o others All other users
a all All users, equivalent to ugo
operator (symbolic mode table)
Operator Description
+ Add permissions for the specified user type
- Remove permissions for the specified user type
= Set the specified user's permissions (reset)

who	User Type	Description
u	user	File owner
g	group	Users in the same group
o	others	All other users
a	all	All users, equivalent to ugo

Operator	Description
+	Add permissions for the specified user type
-	Remove permissions for the specified user type
=	Set the specified user's permissions (reset)

permission (symbolic mode table)

Mode	Name	Description
r	Read	Set read permission
w	Write	Set write permission
x	Execute	Set execute permission
X	Special Execute	Set execute permission only if the file is a directory or if other users have execute permission
s	Setuid/gid	Set setuid or setgid permission when the file is executed, depending on the who parameter specified
t	Sticky Bit	Set the sticky bit; only the superuser can set this, and only the file owner can use it

Examples

chmod a+r file             # Add read permission for all users to the file
chmod a-x file             # Remove execute permission for all users from the file
chmod a+rw file            # Add read and write permissions for all users to the file
chmod +rwx file            # Add read, write, and execute permissions for all users to the file
chmod u=rw,go= file        # Set read and write permissions for the file owner and clear all permissions for the user group and                               other users (space indicates no permission)
chmod -R u+r,go-r LUCKFOX  # Add read permissions for the user to the file and its subdirectory hierarchy, and remove read                                     permissions for the user group and other users

Numeric Mode
- Octal Syntax
  # Permission rwx Binary
  7 Read + Write + Execute rwx 111
  6 Read + Write rw- 110
  5 Read + Execute r-x 101
  4 Read r-- 100
  3 Write + Execute -wx 011
  2 Write -w- 010
  1 Execute --x 001
  0 None --- 000
- For example: Explanation of 765:
  - Numeric representation of owner's permissions: The sum of the numbers of the owner's three permission bits. For example, rwx, which is 4 + 2 + 1, should be 7.
  - Numeric representation of group's permissions: The sum of the numbers of the group's permission bits. For example, rw-, which is 4 + 2 + 0, should be 6.
  - Numeric representation of other users' permissions: The sum of the numbers of the other users' permission bits. For example, r-x, which is 4 + 0 + 1, should be 5.
- Common numeric permissions
  - 400 - r-- --- --- Owner can read, others can't do anything.
  - 644 - rw- r-- r-- Owner and group can read, only owner can edit.
  - 660 - rw- rw- --- Owner and group can read and write, others can't do anything.
  - 664 - rw- rw- r-- Everyone can read, but only owner and group can edit.
  - 700 - rwx --- --- Owner can read, write, and execute, others can't do anything.
  - 744 - rwx r-- r-- Everyone can read, but only owner can edit and execute.
  - 755 - rwx r-x r-x Everyone can read and execute, but only owner can edit.
  - 777 - rwx rwx rwx Everyone can read, write, and execute (not recommended).
- Examples
```
chmod 664 file  # Add read permission for all users, owner and group have edit permission
```

#	Permission	rwx	Binary
7	Read + Write + Execute	rwx	111
6	Read + Write	rw-	110
5	Read + Execute	r-x	101
4	Read	r--	100
3	Write + Execute	-wx	011
2	Write	-w-	010
1	Execute	--x	001
0	None	---	000

tar

Command Function

The tar command is a utility for creating and extracting backup files. It can unpack files contained in an archive. While tar itself does not compress files, it can be combined with compression tools (like gzip or bzip2) to create compressed archives (e.g., .tar.gz or .tar.bz2).

Command Format

tar [options] -f luckfox.tar [file/directory]

Parameter Descriptions

Parameter	Description
options	-x	Extract files from an archive
	-c	Create a new archive
	-v	Show detailed operation progess
	-f	Specify the name of the archive file (must be the last option in the list)
	-z	Use gzip for compression or decompression
	-j	Use gzip for compression or decompression
	-J	Use xz for compression or decompression
file/directory	The target file or directory to compress or extract

Usage Examples

Create Compressed Files

tar -czvf luckfox.tar.gz 1.txt 2.txt 3.txt directory   # Compress files and directories using gzip
tar -cjvf luckfox.tar.bz2 directory                    # Compress using bzip2
tar -cJvf luckfox.tar.xz directory                     # Compress using xz

Extract Compressed Files

tar -xzvf luckfox.tar.gz                              # Extract gzip-compressed files
tar -xjvf luckfox.tar.bz2                             # Extract bzip2-compressed files
tar -xJvf luckfox.tar.xz                              # Extract xz-compressed files

find

Command Function

The find command is used to search for files in a specified directory. Any string preceding the options is considered the directory name to search. If no options are specified, find searches the current directory for subdirectories and files, displaying all found items.

Command Format

find [path][match condition] [action]

Command Format

Parameter	Description
path	The directory path to search. Can include multiple paths separated by spaces. Defaults to the current directory if unspecified.
match condition	Specifies search criteria, such as filename, file type, or size.
action	Specifies actions to perform on matched files, like deleting or copying.

Usage Examples

Find a file by name (e.g., searching for luckfox.py):
```
sudo find -name luckfox.py 
```

Search within specific directory depths:

sudo find /etc/ -maxdepth 1 -name *.conf   # Search up to 1 level deep in /etc for .conf files
sudo find /etc/ -mindepth 2 -name *.conf   # Search within subdirectories of /etc, starting from depth 2

List files updated in the last 20 days:
```
sudo find . -ctime -20
```

Find files with specific permissions:

sudo find . -type f -perm 644 -exec ls -l {} \;

List zero-length files with their full paths:

sudo find / -type f -size 0 -exec ls -l {} \;

cat

Command Function

The cat command is used to concatenate files and display their contents on the standard output. Its primary purposes are viewing and combining files

Command Format

cat [options][file]

Parameter Description

Parameter	Description
options	`-n`: Display line numbers, adding a number to each line of output.
file	File name.

Usage Examples

Display the contents of the test.txt file in the terminal:
```
cat test.txt
```
List the contents of all .txt files in the current directory:
```
cat *.txt 
```
Append standard input to the end of the file:
```
cat >> file
```
Redirect standard input to file, overwriting its content:
```
cat > file
```
Combine the contents of file1 and file2 into file3:
```
cat file1 file2 > file3
```

grep

Command Function

As one of the Linux "text-processing trinity" (along with sed and awk), the grep command searches for patterns in a file or stream, listing all occurrences of a specific string or pattern.

Command Format

grep [options] pattern [files]

Parameter Description

Parameter	Description
options	-i	Ignore case while matching.
	-v	Perform inverse matching, displaying non-matching lines.
	-n	Display the line number of matching lines.
	-r	Recursively search files in subdirectories.
	-l	Display only the names of matching files.
	-c	Display only the count of matching lines.
pattern	The string or regular expression to search for.
files	File(s) to search, allowing multiple files.

Usage Examples

Search for files containing the string sys in the current directory:
```
ls | grep sys
```
Search config.txt for lines starting with arm using a regular expression:
```
grep ^arm config.txt
```
Find and display lines containing test in files with names ending in file:
```
grep test *file
```
Recursively search the dir folder for lines matching the regular expression luckfox, displaying filenames and line numbers:
```
grep -r -n luckfox dir/
```

ifconfig

Command Function

The ifconfig command is used to view and configure network devices. It allows you to adapt network settings in response to environmental changes. Note: Configurations made using ifconfig are not persistent and will be lost after a restart unless written to the appropriate network configuration files.

Usage Examples

sudo ifconfig eth0          # View wired network IP address
sudo ifconfig wlan0         # View wireless network IP address

apt

Command Function

Popular Linux distributions provide centralized package management tools to search, install, and manage software stored in repositories. The apt command allows efficient management of software packages in Ubuntu and Debian-based systems.

Command Format

apt [options][command] [package ...]

Parameter Description

Parameter	Description
options	Options like `-h` (help), `-y` (auto-confirm), and `-q` (suppress output).
command	The action to perform (e.g., install, remove).
package	The name of the package to manage.

Usage Examples

The local database stores the list of available remote package repositories. Therefore, it is recommended to update this database before installing or upgrading packages using the following command:
```
sudo apt-get update
```
After updating, you can install software by its name using the following command:
```
sudo apt-get install XXX -y     # -y skips the confirmation prompt
```
Without a package management system, keeping Linux-installed software up-to-date is a significant task. Administrators and users must manually track upstream software updates and security warnings. With a package manager, you can use just a few commands to ensure software remains current:
```
sudo apt-get upgrade            # Updates installed packages
sudo apt-get dist-upgrade       # Upgrades the system to the latest version (use cautiously)
```

Both upgrade and dist-upgrade upgrade installed packages. However, the apt-get upgrade command cannot install new packages or remove existing ones, while dist-upgrade can install new packages or remove existing ones if necessary.

Since the package manager tracks which files are provided by which packages, you can achieve a clean system after uninstalling unnecessary packages with the following commands:

# Command to remove a package
sudo apt remove <package_name>
# Clean up unused dependencies and library files
sudo apt autoremove
# Remove a package and its configuration files
sudo apt purge <package_name>

dpkg

Command Function

The Debian system package format is .deb. To install .deb packages directly, the dpkg command is used.

Usage Examples

Install a package:
```
sudo dpkg -i package.deb
```
Uninstall a package:
```
sudo dpkg -r package_name
```

shutdown & reboot

It is not recommended to unplug the power cord directly for Omni3576. If you boot from a TF card, unplugging the power cord directly might cause data loss or corruption on the TF card as some data in memory may not have been written to the TF card. This could result in system startup failures. Use the following commands instead:
```
sudo shutdown -h now         # Shut down immediately
sudo shutdown -r now         # Reboot the system
sudo shutdown -h 10          # Shut down after 10 minutes
sudo reboot                  # Reboot (commonly used)
```
Regardless of the command used to shut down the system, root user privileges are required. If using a regular user account like "luckfox," you can temporarily gain root privileges by using the sudo command.

6. Rockchip Common Commands

Check the NPU driver version:
```
cat /sys/kernel/debug/rknpu/version
```
Check the unique chip serial number:
```
cat /proc/cpuinfo | grep Serial
```

Check the CPU temperature.

echo "$(cat /sys/class/thermal/thermal_zone0/temp) / 1000" | bc

1. Introduction​

2. Terminal Overview​

3. Linux File Structure​

4. File System​

4.1 inode and block Overview​

4.2 inode Considerations​

4.3 Symbolic Links vs. Hard Links​

5. Frequently Used Linux Commands​

ls​

Command Function​

Command Format​

Parameter Description​

Usage Examples​

cd​

Command Function​

Command Format​

Parameter Description​

Usage Examples​

pwd​

Command Function​

Usage Examples​

df​

Command Function​

Usage Examples​

touch​

Command Function​

Usage Examples​

mkdir​

Command Function​

Command Format​

Parameter Description​

Usage Examples​

cp​

Command Function​

Command Format​

Parameter Description​

Usage Examples​

mv​

Command Function​

Command Format​

Parameter Description​

Usage Examples​

rm​

Command Function​

Command Format​

Parameter Description​

Usage Examples​

chmod​

Command Description​

Command Explanation​

tar​

Command Function​

Command Format​

Parameter Descriptions​

Usage Examples​

find​

Command Function​

Command Format​

Command Format​

Usage Examples​

cat​

Command Function​

Command Format​

Parameter Description​

Usage Examples​

grep​

Command Function​

Command Format​

Parameter Description​

Usage Examples​

ifconfig​

Command Function​

Usage Examples​

apt​

Command Function​

Command Format​

Parameter Description​

Usage Examples​

dpkg​

Command Function​

1. Introduction

2. Terminal Overview

3. Linux File Structure

4. File System

4.1 inode and block Overview

4.2 inode Considerations

4.3 Symbolic Links vs. Hard Links

5. Frequently Used Linux Commands

ls

Command Function

Command Format

Parameter Description

Usage Examples

cd

Command Function

Command Format

Parameter Description

Usage Examples

pwd

Command Function

Usage Examples

df

Command Function

Usage Examples

touch

Command Function

Usage Examples

mkdir

Command Function

Command Format

Parameter Description

Usage Examples

cp

Command Function

Command Format

Parameter Description

Usage Examples

mv

Command Function

Command Format

Parameter Description

Usage Examples

rm

Command Function

Command Format

Parameter Description

Usage Examples

chmod

Command Description

Command Explanation

tar

Command Function

Command Format

Parameter Descriptions

Usage Examples

find

Command Function

Command Format

Command Format

Usage Examples

cat

Command Function

Command Format

Parameter Description

Usage Examples

grep

Command Function

Command Format

Parameter Description

Usage Examples

ifconfig

Command Function

Usage Examples

apt

Command Function

Command Format

Parameter Description

Usage Examples

dpkg

Command Function