SUSE Linux Enterprise Desktop Administration Chapter 7 Manage Directories and Files.

SUSE Linux Enterprise Desktop Administration

Chapter 7Manage Directories and Files


Objectives

• Objective 1—Understand the File System Hierarchy Standard (FHS)

• Objective 2—Identify File Types in the Linux System• Objective 3—Change Directories and List Directory

Contents

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Objectives (continued)

• Objective 4—Create and View Files• Objective 5—Work with Files and Directories• Objective 6—Find Files on Linux

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Objective 1—Understand the File System Hierarchy Standard (FHS)

• The file system concept of Linux is considerably different than that of other operating systems

• A filename in Linux can be up to 255 characters long– Can contain any number of special characters

• You can also use umlauts, letters with diacritical marks, or other country-specific characters

• Linux differentiates between uppercase and lowercase letters

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The Hierarchical Structure of the File System

• Linux file system involves a hierarchical file system that can be depicted in the form of a tree

• Tree is not limited to a local partition– Can stretch over several partitions, which can be

located on different computers in a network– Begins at the root

• A file in the tree is uniquely defined by its path• Path refers to the directory names that lead to a file

– Relative path– Absolute path

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SUSE Linux Enterprise Desktop Administration 6

Figure 7-1 Linux hierarchical file system

The Hierarchical Structure of the File System (continued)


The Hierarchical Structure of the File System (continued)

• The absolute path always begins with a slash (‘‘/’’), the symbol for the root directory

• You can change directories with the cd command– Using both absolute and relative paths

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FHS (Filesystem Hierarchy Standard)

• The structure of the file system is described in the Filesystem Hierarchy Standard (FHS)– Specifies which directories must be located on the first

level after the root directory and what they contain• The FHS defines a two-layered hierarchy:

– The directories in the top layer (immediately below the root directory ‘‘/’’)

– As a second layer, the directories under /usr and /var

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Root Directory (/)

• The root directory refers to the highest layer of the file system tree– Normally only directories (not files) are located here

• When the system is booted, the partition on which this directory is located is the first one mounted

• The following directories always have to be on the same partition as the root directory:– /bin, /dev, /etc, /lib, and /sbin

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Essential Binaries for Use by All Users (/bin)

• /bin contains executable programs that are required when no other file systems are mounted

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Table 7-1 Some of the programs in the /bin directory


Boot Directory (/boot)

• Contains static files of the boot loader GRUB• The backed-up information for the Master Boot

Record (MBR) and the system map files are also stored here

• Also contains the kernel that has the filename vmlinuz

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Other Partitions (/data)

• If YaST finds other (non-Windows) partitions or another hard disk during the installation– Creates mountpoints for each partition labeled:

• /data1• /data2• /dataX

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Device Files (/dev)

• Each hardware component existing in the system is represented as a file in the /dev directory

• Two kinds of device files are included:– Character-oriented device files– Block-oriented device files

• Major device numbers– Connection to device drivers in the kernel is

implemented via numbered channels• Corresponding to the number of the device driver in

question

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Device Files (/dev) (continued)

• A driver might be responsible for several devices of the same type– To distinguish between these devices, the minor

device number is used• Most device files are created dynamically by udev

in /dev– When the corresponding hardware is detected during

the boot process• The null device /dev/null is also located in this

directory

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SUSE Linux Enterprise Desktop Administration 15Table 7-2 Some important device files


Configuration Files (/etc)

• The /etc directory and its subdirectories contain system configuration files– Almost all of them can be processed with any editor

• Normal users can read nearly all of these files, but they cannot edit any of them– According to the FHS, no executable programs can be

located here– Subdirectories contain many shell scripts

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Table 7-3 Some important configuration files


User Directories (/home)

• Home directory– Every user on a Linux system has his or her own area

in which to work with files• Individual configuration files can be found in the

user’s home directory– These configuration files are hidden files– All these files have names that begin with a dot

• The home directory of a user can also be addressed via the shortcut “~”

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Table 7-4 Some important files in a user’s home directory


Libraries (/lib)

• Many programs use specific functions that are also used by other programs– Functions are removed from the actual program, stored

in the system, and only called up when the program runs

• Called shared libraries

• The /lib directory contains the libraries that are used by programs in the /bin and /sbin directories

• The kernel modules are located in the /lib/modules/ directory– Find additional libraries below the directory /usr

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Mountpoints for Removable Media (media/*)

• SUSE Linux creates directories in the /media/ directory for removable media it detects:– /media/floppy/—Created for a floppy disk drive– /media/cdrom/—Created for a CD-ROM drive– /media/cdrecorder—Created for a CD burner– /media/dvd—Created for a DVD drive– /media/usbdisk/—Created for a USB stick– /media/medianame—Created after inserting a labeled

removable media

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Application Directory (/opt)

• Installed programs can store their static files in the /opt directory

• First, a directory with the name of the application is created– The files are then stored in that directory

• Examples include GNOME (/opt/gnome) and KDE (/opt/kde3)

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Home Directory of the Administrator (/root)

• The home directory of the system administrator should be on the same partition as the root directory, ‘‘/’’

• Only then is it guaranteed that the user root can:– Always log in without a problem– Have his or her own configured environment available

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System Binaries (/sbin)

• The /sbin directory contains important programs for system administration

• Programs that are run by normal users are also located in /bin

• Programs in the /sbin directory can also, as a rule, be run by normal users– But only to display the configured values

• Changes to the configuration can only be made by the user root

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Table 7-5 An overview of important files in the /sbin directory

System Binaries (/sbin) (continued)


Data Directories for Services (/srv)

• The subdirectories of the /srv directory contain data of various services

• Examples:– The files of the Apache Web server are located in

the /srv/www/ directory– The FTP server files are located in the /srv/ftp/

directory

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Temporary Area (/tmp)

• Various programs create temporary files that are stored in /tmp until they are deleted

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The Hierarchy Below /usr

• The /usr directory, in accordance with the FHS, represents a second hierarchical layer

• This is the location for all application programs, graphical interface files, additional libraries, locally installed programs, and commonly shared directories containing documentation

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Figure 7-6 Some of the important files in the /usr directory

The Hierarchy Below /usr (continued)


Variable Files (/var)

• The /var directory and its subdirectories contain files that can be modified while the system is running

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Figure 7-7 Some of the most important directories beneath /var


Windows Partitions (/windows)

• If YaST finds any partitions with a Microsoft file system, it automatically creates a /windows directory

• Inside this directory: subdirectories labeled with Windows drive characters

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Process Files (/proc)

• Linux handles process information that is made available to users via the /proc directory

• The /proc directory is generated dynamically when it is accessed– Contains files and directories– Each process has its own directory

• /proc also includes directories and files containing information about the state of the system

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SUSE Linux Enterprise Desktop Administration 33Figure 7-8 Some of the important files in the /proc directory

Process Files (/proc) (continued)


System Information Directory (/sys)

• The /sys directory provides information, in the form of a tree structure, on various hardware buses, hardware devices, active devices, and their drivers

• Like the /proc directory, /sys is generated dynamically when it is accessed

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Mountpoint for Temporarily Mounted File Systems (/mnt)

• The standard directory for integrating file systems is /mnt– Should only be used for temporary purposes– For permanent mounts, you should create an

appropriately named directory• Mount hard drive partitions using the mount

command• To remove a partition, use the umount command• If the file system format is not supported by the

kernel, the command is aborted35


Directories for Mounting Other File Systems

• A directory must exist at the point where you intend to mount the file system– Referred to as the mount point

• In most cases, only the user root can mount and unmount directories– Removable media can be changed by a normal user

• The file /etc/mtab shows which file systems are currently mounted

• You can also share certain directories with many computers

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Table 7-9 Directories that can be shared

Directories for Mounting Other File Systems (continued)

Table 7-10 Directories that cannot be imported from other computers


Exercise 7-1: Explore the SUSE Linux File System Hierarchy

• In this exercise, describe what directories the characters / and ~ refer to – Then, find out the mount point of the DVD– Mount the DVD manually at another position (/mnt) in

the file system

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Objective 2—Identify File Types in the Linux System

• Available file types:– Normal Files– Directories– Device Files– Links– Sockets– FIFOs

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Normal Files

• Refer to files as they are also known in other operating systems:– Sets of contiguous data addressed with one name

• The names for such files can be freely chosen and there is no division into filename and file type

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Directories

• Directories are used to organize files and directories into groups

• Directories contain two entries with which the structure of the hierarchical file system is implemented– One of these entries (‘‘.’’) points to the directory itself – The other entry (‘‘..’’) points to the entry one level

higher in the hierarchy

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Device Files

• Each piece of hardware in a Linux system is represented by a device file– With the exception of network cards

• Every program that wants to access hardware must access it through the corresponding device file– The programs write to or read from a device file

• The kernel then ensures that the data finds its way to the hardware or can be read from the file

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Links

• Links are references to files located at other points in the file system

• Data maintenance is simplified through the use of such links– Changes only need to be made to the original file– The changes are then automatically valid for all links

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Sockets

• A socket refers to a special file in the file system – Implements data exchange between two locally

running processes

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FIFOs

• FIFO (First In First Out) or ‘‘named pipe’’– Files that are used to exchange data between

processes• A FIFO file can only exchange data in one direction

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Objective 3—Change Directories and List Directory Contents

• You can use the following commands to change the active directory and list the contents of a directory:– cd– ls– pwd

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cd

• You can use the cd (change directory) command to change between directories

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Table 7-11 Examples of the cd command


ls• The ls (list) command lists the specified files

48Table 7-12 The most important options of the ls command


pwd

• You can use the pwd (print working directory) command to display the path of the current directory

• If you enter pwd with the -P option, pwd prints the physical directory without any symbolic links

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Exercise 7-2: Change Directories and List Directory Contents

• In this exercise, describe what directories the characters . and .. refer to

• Then, change between directories (cd), display the name of the active directory (pwd), and list directory contents (ls)

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Objective 4—Create and View Files

• To create and view files, you need to know how to do the following:– Create a New File with touch– View a File with cat– View a File with less– View a File with head and tail

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Create a New File with touch

• You can use the touch command to change the time stamp of a file– Or create a new file with a size of 0 bytes

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Table 7-13 The most important options of the touch command


View a File with cat

• You can use the cat (concatenate) command to view the contents of a file– The command must include the filename of the file

you want to see

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View a File with less

• You can use the less command to display the contents of a file page by page– Even compressed files (such as .gz and .bz2) can be

displayed

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View a File with less (continued)

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Table 7-14 Keystrokes used with the less command


View a File with head and tail

• With the head command, you can view only the first few lines of a file

• The tail command shows you only the last few lines of a file

• By default, these commands only show 10 lines• When used with the tail command, the option -f

displays a continuously updated view of the last lines of a file

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Exercise 7-3: Create and View Files

• In this exercise, create an empty new_file file• Then, display the content of the /var/log/messages

file in the following ways:– At once with the cat command– Page by page with the less command; then, look for

the word root in the file– In the first five lines with the head command– In the last lines continuously updated with the tail

command– To view new log data, log in and log out as root

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Objective 5—Work with Files and Directories

• In this objective, you learn how to do the following:– Copy, Move, and Rename Files and Directories– Create Directories– Delete Files and Directories– Link Files

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Copy, Move, and Rename Files and Directories

• Move and rename files with mv– You can use the mv (move) command to move one or

more files to another directory

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Table 7-15 The options of the mv command


Copy, Move, and Rename Files and Directories (continued)

• Copy files with cp– You can copy files and directories with the cp (copy)

command– When using the command cp, remember the

following:• cp overwrites existing files without confirmation• Avoid automatic overwriting by using the option –i

– If you want to copy just the contents of a directory, the target directory must already exist

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Copy, Move, and Rename Files and Directories (continued)

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Table 7-16 The options of the cp command


Create Directories

• You can use the mkdir (make directory) command to create new directories

• The option -p lets you create a complete path, as in the following example:– mkdir --p proposal/january

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Delete Files and Directories

• Use rmdir to delete empty directories– You can use the rmdir (remove directory) command

to remove the indicated directory or directories• Use rm to delete files and directories

– You can use the rm (remove) command to delete files without being asked for confirmation

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Delete Files and Directories (continued)

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Table 7-17 The options of the rm command


Exercise 7-4: Copy, Move, and Delete Files, Create and Delete Directories

• In this exercise, copy and move files with the cp and mv commands, create new directories with the mkdir command, and delete files and directories with the rm and rmdir commands

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Link Files

• File system formats in Linux keep data and administration information separate

• Each file is described by an inode (index node or information node)– To see the inode number, you can enter ls –i– Each inode is 128 bytes and contains all the

information about this file apart from the filename• The ln command creates a link

– A link is a reference to a file

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Link Files (continued)

• Linux recognizes two kinds of links:– Hard links– Symbolic links

• You create a hard link by using the ln command, which points to the inode of an already existing file– Hard links can only be used when both the file and the

link are in the same file system• You can create a symbolic link with the ln command

and the option –s– A symbolic link is assigned its own inode

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Link Files (continued)

• With symbolic links, the limits of the file system can be overcome

• The disadvantage is that a symbolic link can point to a nonexisting object

• An advantage of symbolic links is that you can create links to directories

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Exercise 7-5: Link Files

• In this exercise, create a symbolic link to the ~/my_file file and a hard link to the ~/my_file1 file with the ln command

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Objective 6—Find Files on Linux

• Two wildcards– ‘‘?’’ (for any character)– ‘‘*’’ (for none, one, or several characters)

• The following tools are introduced in this objective:– graphical search tools– find– which– type

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Graphical Search Tools

• If you enter search in the More Application search bar, you find two applications:– The Desktop Search Tool (Search)– The GNOME Search Tool (Search for Files)

• Search (Search)– When you enter a search term into the Desktop

Search Tool, a list of documents that contain the search term appears as soon as you stop typing

– Desktop Search Tool can be configured by selecting Search > Preferences

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Figure 7-3 The Desktop Search Tool


Figure 7-4 Configuring the Desktop Search Tool


Graphical Search Tools (continued)

• Search (Search) (continued)– The Indexing tab allows you to configure what is

included in or excluded from the search index– See Figure 7-5

• Search for files (GNOME Search Tool)– Allows you to search for information such as file size,

date, or file owner– See Figures 7-6 and 7-7

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SUSE Linux Enterprise Desktop Administration 75Figure 7-5 Configuring the Desktop Search Tool


Figure 7-6 The GNOME Search Tool



Figure 7-7 More options for the GNOME Search Tool



find

• To search for files on the command line, you can use the find command

• Syntax for the find command:– find path criterion action

• Actions include the following:– print (default)– exec command

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Table 7-19 The properties the file should have


which

• The which command searches all paths listed in the variable PATH for the specified command– Returns the full path of the command

• The PATH variable contains the directories where the shell looks for executable files

• You use which if you want to know which program is executed– When the command is entered without specifying a

path

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type

• The type command command can be used to find out what kind of command is executed– When command is entered

• The option -a delivers all instances of a command bearing this name in the file system

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Exercise 7-6: Find Files on Linux

• In this exercise, find files with the whereis, which, and find commands and with the GNOME Search Tool

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Summary

• The Linux file system is arranged hierarchically using a series of directories to store files

• Regardless of the number of file systems, there is only one root directory in Linux, denoted by a ‘‘/’’ character

• Linux directories and files follow the Filesystem Hierarchy Standard (FHS) and their location can be described using absolute or relative pathnames

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Summary (continued)

• The /bin and /sbin directories contain executable binary programs

• The /boot directory contains information used to load the Linux kernel

• The /dev directory contains character and block-oriented device files that are used to identify most hardware devices on the Linux system

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Summary (continued)

• Most system configuration information is stored in text files under the /etc directory and shared libraries are stored under the /lib directory

• Home directories are typically located under the /home directory

• The /media and /mnt directories typically contain mount point subdirectories

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Summary (continued)

• There are many types of files that can exist on the Linux file system

• Text files are the most common file type; contents can be viewed by several utilities

• There are many file management commands• Files can be a link to another file by name or by inode• You can find files on the file system using a variety of

utilities

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SUSE Linux Enterprise Desktop Administration Chapter 7 Manage Directories and Files.

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Transcript of SUSE Linux Enterprise Desktop Administration Chapter 7 Manage Directories and Files.