Bài giảng Quản trị Linux: Basic system administration - Đặng Thanh Bình

Đặng Thanh Bình

Basic System Administration


Contents
• File and Directory management
– ls, cd, pwd, mkdir, mv cp, rm, rmdir, locate, find,
grep
– touch, cat
– Recursive and interactive modes
– PATH variable, which command

• Linking Files
• File and directory permissions
• sudoers
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FILE AND DIRECTORY MANAGEMENT

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The Linux Directory Structure
• Directory: Used to organize other files into a
logical tree structure
– Stored in a filesystem of a specific partition in
the hard disk

• Root: The top level directory

– Referred to using the / character

• Forms root of a hierarchical tree

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The Linux Directory Structure
• The Windows file system structure

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The Linux Directory
Structure
• The Linux file system structure

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File Types
• 4 basic file types
– Normal files (program, text, library, …)
– Directory
– Special files (device, socket, pipe, …)
– Symbolic links (symlinks)

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File Name Regulations
• Maximum 255 characters
• May contain any characters
special characters)

(including

• Hidden file/directory starts with a period (.)

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Pathname
• Absolute pathname: starts with “/”
• Relative pathname: DOES not start with a
“/”
• Special pathnames:
• .. – parent directory
• . – current directory
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Changing Directories
• Home directory: unique to each user
– ~ metacharacter used to refer to home directory

• pwd (print working directory) command:
displays current directory in the directory tree
• cd (change directory) command: change the
current directory in the directory tree

– Argument specifies the destination directory
– cd: go to user’s home directory
– cd PATHNAME
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Listing Files
• ls command: List the files in a directory
• May pass an argument indicating the
directory to be listed
– –F option: Argument to indicate file types
– –l option: Argument to list long file listings

Long listing for each file
includes
eight
components
• File type character
• List of permissions (mode
of the file)
• Hard link count

•
•
•
•

Owner
Group owner
File size

Most recent modification
time
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• Filename


Listing Files

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Listing Files

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Creating Files
• touch command: creat an empty file
– touch FILENAME
– touch FILE1 FILE2

• cat command: display and/or edit file
content
– -n option: displays line number and contents
– cat FILENAME
– cat > FILENAME (use Ctrl-D to finish)

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Viewing Text Files
• tac command: displays contents of a text file
in reverse order
• head command: view first ten lines of a file
• tail command: view last ten lines of a file
• For head and tail commands
– Line count includes blank lines
– Can provide numeric option to specify the
number of lines to be displayed (e.g., head -2
filename)
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Viewing Text Files
• more command: displays text files page-bypage
– Pressing Spacebar displays the next page
– Pressing Enter displays the next line

• less command: same as more command,
but can also use cursor to scroll
• Interaction with more and less:
– pressing h key gets Help screen
– pressing q key quits more and less commands
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Viewing Text Files
• more and less can be used with output of
other commands
• If output is too large to fit on terminal

screen, use “|” metacharacter and more or
less command
– e.g., ls -l | more

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Displaying the Contents of Binary Files

• strings command: searches for and displays
text characters in a binary file
– Might indicate purpose of binary file

• od command: displays contents of file in
octal format (numeric base 8 format)
– -x option displays contents of the file in
hexadecimal format (numeric base 16 format)

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Managing Files and Directories
• mkdir command: creates new directories
– Arguments specify
relative pathname

directory’s

absolute

or

• mv command: moves files
– Minimum of two arguments:
• Source file/directory (may specify multiple sources)
• Target file/directory

– Pathnames can be absolute or relative
– For multiple files, can use wildcards in pathname
– Also used to rename files or directories
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Managing Files and Directories
• cp command: copies files
– Same arguments as the mv command
– Also used to make copies of files

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Managing Files and Directories
• Recursive: referring to itself and its own
contents
– Recursive copy command copies the directory and all
subdirectories and contents
– Recursive search includes all subdirectories in a
directory and their contents
– Use –r option

• Interactive mode:
overwriting files

Prompts

user

before

– –i option
– –f option (force): Overrides interactive mode
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Managing Files and Directories
• rm command: Removes files
– Arguments are a list of files
– Can use wildcards
– Interactive mode by default
– Use -f option to override

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Managing Files and Directories
• rmdir command: removes directories
– Arguments are a list of files
– Can use wildcards
– Interactive mode by default
– Use -f option to override

– Cannot be used to remove directory full of files

• To delete directory and all its contents
(subdirectories and files), use rm –r
command
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Finding Files
• locate command: Search for files on system
– Receives full or partial filename as argument
– Uses premade indexed database of all files on
system
• To update the database use updatedb command

– Information returned may not fit on screen
• Use with more or less commands

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Finding Files
• find command: recursively search for files
starting from a specified directory
– Slower than locate command, but more versatile
– Format: find <start directory> -criteria find>
• e.g., find /root –name project

– If using wildcard metacharacters, ensure that they

are interpreted by the find command
• Place wildcards in quotation marks

– To reduce search time, specify subdirectory to be
searched
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