Getting Started with Linux: Novells Guide to CompTIAs Linux Course 3060

1
Getting Started with Linux Novells Guide to
CompTIAs Linux (Course 3060)

• Section 5
• Manage Directories and Files in Linux

2
Objectives

• Understand the Filesystem Hierarchy Standard
  (FHS)
• Identify File Types in the Linux System
• Change Directories and List Directory Contents
• Create and View Files

3
Objectives (continued)

• Manage Files and Directories
• Find Files
• Search File Content
• Archive, Back up, Compress, and Decompress Files

4
Understand the Filesystem Hierarchy Standard (FHS)

• The file system concept of Linux (and, in
  general, of all UNIX systems) is considerably
  different than that of other operating systems
• To understand the concept of the Linux file
  system, you need to know the following
• The Hierarchical Structure of the File System
• FHS (Filesystem Hierarchy Standard)
• Root Directory /
• Essential Binaries for Use by All Users (/bin/)
• Boot Directory (/boot/)

5
Understand the FHS (continued)

• To understand the concept of the Linux file
  system, you need to know the following
  (continued)
• Device Files (/dev/)
• Configuration Files (/etc/)
• User Directories (/home/)
• Libraries (/lib/)
• Mount Points for Removable Media (/media/)
• Application Directory (/opt/)
• Home Directory of the Administrator (/root/)
• System Binaries (/sbin/)
• Data Directories for Services (/srv/)

6
Understand the FHS (continued)

• To understand the concept of the Linux file
  system, you need to know the following
  (continued)
• Temporary Area (/tmp/)
• The Hierarchy below /usr/
• Variable Files (/var/)
• Process Files (/proc/)
• System Information Directory (/sys/)
• Mount Point for Temporarily Mounted File Systems
  (/mnt/)
• Directories for Mounting Other File Systems

7
The Hierarchical Structure of the File System
8
The Hierarchical Structure of the File System
(continued)
9
FHS (Filesystem Hierarchy Standard)

• The structure of the file system is described in
  the Filesystem Hierarchy Standard (FHS)
• It specifies which directories must be located on
  the first level after the root directory and what
  they contain
• It does not specify all details
• 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/

10
Root Directory /

• The root directory refers to the highest layer of
  the file system tree
• Only directories are located here, not files
• When the system is booted, the partition on which
  this directory is located is the first one
  mounted
• All programs that are run on the system start
  must be available on this partition
• The following directories always have to be on
  the same partition as the root directory
• /bin/, /dev/, /etc/, /lib/, and /sbin/

11
Essential Binaries for Use by All Users (/bin/)
12
Boot Directory (/boot/)

• /boot/ contains static files of the boot loader
• These are files required for the boot process
  (with the exception of configuration files)
• The backed-up information for the Master Boot
  Record (MBR) and the system map files are also
  stored here
• These contain information about where exactly the
  kernel is located on the partition
• This directory also contains the kernel
• According to FHS, the kernel can also be located
  directly in the root directory

13
Device Files (/dev/)

• Each hardware component existing in the system is
  represented as a file in /dev/
• An exception is network cards
• Character-oriented device files
• Block-oriented device files
• Major device numbers The connection to device
  drivers in the kernel is implemented via numbered
  channels, which correspond to the number of the
  device driver in question
• Minor device number A driver might be
  responsible for several devices of the same type
• /dev/null is also located here

14
Device Files (/dev/, continued)
Use mknod to generate special device files for
specific devices.
15
Device Files (/dev/, continued)
16
Configuration Files (/etc/)
17
User Directories (/home/)

• Every user on a Linux system has his own area in
  which to create and remove files its home
  directory
• Individual configuration files can be found in
  the users home directory
• If there are no special settings, the home
  directories of all users are located beneath
  /home/
• The home directory of a user be addressed via

18
Libraries (/lib/)

• Shared libraries are removed from the actual
  program, stored in the system, and only called up
  when the program runs
• The directory /lib/ contains the libraries that
  are used by programs in the directories /bin/ and
  /sbin/
• The kernel modules (hardware drivers not compiled
  into the kernel) are located in the directory
  /lib/modules/
• You can find additional libraries below the
  directory /usr/

19
Mount Points for Removable Media (/media/)

• SUSE Linux creates directories such as the
  following in the directory /media/ (depending on
  your hardware) for mounting removable media
• /media/cdrom/
• /media/cdrecorder/
• /media/dvd/
• /media/floppy/

20
Application Directory (/opt/)

• Installed programs can store their static files
  in the directory /opt/
• 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 KDE3
  (/opt/kde3/)

21
Home Directory of the Administrator (/root/)

• The home directory of the system administrator is
  not located beneath /home/ like that of a normal
  user
• Preferably, it 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 and have her own
  configured environment available

22
System Binaries (/sbin/)

• Contains important system administration programs
• Programs in /sbin/ can also, as a rule, be run by
  normal users, but only to display configured
  values

23
System Binaries (/sbin/, continued)
24
Data Directories for Services (/srv/)

• The directory /srv/ contains subdirectories
  filled with data of various services
• For example
• The files of the Apache web server are located in
  the directory /srv/www/
• The FTP server files are located in the directory
  /srv/ftp/

25
Temporary Area (/tmp/)

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

26
The Hierarchy below /usr/

• According with the FHS, represents a second
  hierarchical layer

27
The Hierarchy below /usr/ (continued)
28
Variable Files (/var/)

• Contains a hierarchy described in the FHS
• This directory and its subdirectories contain
  files that can be modified while the system is
  running

29
Variable Files (/var/, continued)
30
Process Files (/proc/)
Generated dynamically when accessed
init always has the process number 1
31
Process Files (/proc/, continued)
32
Process Files (/proc/, continued)
33
System Information Directory (/sys/)

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

34
Mount Point for Temporarily Mounted File Systems
(/mnt/)

• Standard directory for integrating file systems
• It should only be used for temporary purposes
• da10 mount /dev/hda7 /mnt
• da10 umount /mnt
• If you do not include any options with mount, the
  program tries out several file system formats
• To specify a specific file system, use the option
  -t
• If the file system format is not supported by the
  kernel, the command is aborted, and you receive
  an error message
• In this case, you must compile a new kernel that
  supports the file system format

35
Directories for Mounting Other File Systems

• A directory must exist at the point where you
  intend to mount the file system
• This directory is referred to as the mount point
• In most cases, only the user root can mount and
  unmount directories
• Use mount and umount
• /etc/mtab shows which file systems are mounted
• If you mount a file system to a non-empty
  directory, existing contents of directory will
  not be accessible
• Mounted file system does not have to be on a
  local hard disk

36
Directories for Mounting Other File Systems
(continued)

• The directories listed below cannot be imported
  from other machines
• Some of the directories that can be shared are

37
Exercise 5-1 Mount Removable Media

• In past versions of Linux, it was necessary to
  mount removable media with some command to access
  them and to unmount them afterwards
• This has been automated in current kernel
  versions
• In this exercise, you access removable media

38
Identify File Types in the Linux System

• The file types in Linux referred to as normal
  files and directories are also familiar to other
  operating systems
• Normal Files
• Directories
• Additional types of files are UNIX-specific
• Device Files
• Links
• Sockets
• FIFOs

39
Normal Files

• Normal files a set of contiguous data addressed
  with one name
• This includes all the files normally expected
  under this term (such as ASCII texts, executable
  programs, or graphics files)
• You can use any names you want for these
  filesthere is no division into filename and file
  type
• A number of filenames still retain this
  structure, but these are requirements of the
  corresponding applications, such as a word
  processing program or a compiler

40
Directories

• 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

41
Device Files

• Each piece of hardware (with the exception of
  network cards) in a Linux system is represented
  by a device file
• These files represent links between the hardware
  components or the device drivers in the kernel
  and the applications
• 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

42
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

43
Sockets

• A socket refers to a special file with which data
  exchange between two locally running processes
  can be implemented through the file system

44
FIFOs

• FIFO (first in first out) or named pipe is a term
  used for files used to exchange data between
  processes
• The file can exchange data in one direction only

45
Change Directories and List Directory Contents

• The prompt of a shell terminal contains the
  current directory (such as tux_at_da10)
• The tilde () indicates that you are in the
  users home directory
• Commands
• ls
• cd
• pwd

46
ls
47
ls (continued)
48
cd

• cd change directory

49
pwd

• pwd print working directory
• pwd -P prints the physical directory without any
  symbolic links

50
Exercise 5-2 Change Directories and List
Directory Contents

• Smooth administration of a Linux system requires
  familiarity with the directory tree and how to
  move within it
• The purpose of this exercise is to show you how
  to orient yourself and move about within that
  tree

51
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

52
Create a New File with touch

• touch changes the time stamp of a file or
  creates a new file with a size of 0 bytes

53
Create a New File with touch (continued)
54
View a File with cat

• You can use cat to view the contents of a file
• Comparable to the command type in DOS
• The command must include the filename of the file
  you want to see

55
View a File with less

• less displays the contents of a file page by page
• Even compressed files (such as .gz and .bz2) can
  be displayed

56
View a File with less (continued)
57
View a File with head and tail

• Used to view the first or last lines of a file
• By default, they show ten lines
• head -20 displays the first twenty lines
• tail -f displays a continuously updated view of
  the last lines of a file

58
Exercise 5-3 Create and View Files

• To be able to view configuration and log files is
  a necessary part of system administration
• Various tools exist for this purpose, and you
  choose the appropriate one depending on whether
  you want to view the complete file or only part
  of it
• In this exercise, you practice creating and
  viewing files or parts of them

59
Manage Files and Directories

• In this objective, you learn how to
• Copy and Move Files and Directories
• Create Directories
• Delete Files and Directories
• Link Files

60
Copy and Move Files and Directories

• Move files with mv
• mv .txt /tmp
• mv recipe new_recipe
• Copy files with cp cp source destination
• If you want to copy just the contents of a
  directory, the target directory must already
  exist
• cp -R /tmp/quarterly-1 /tmp/expenses

61
Copy and Move Files and Directories (continued)
62
Copy and Move Files and Directories (continued)

• To copy the contents of proposals/ and all its
  files, including hidden files and subdirectories,
  to the existing directory proposals_old/
• To avoid copying the hidden files, do the
  following

63
Copy and Move Files and Directories (continued)
64
Exercise 5-4 Copy and Move a File and a Directory

• Copying, moving, and renaming files are basic and
  frequent operations done with files
• Most probably, you are already very familiar with
  these operations on a graphical desktop
  environment
• The purpose of this exercise is to get used to
  performing these operations on the command line

65
Create Directories

• You can use the command mkdir (make directory) to
  create new directories
• mkdir proposal
• Use the option -p to create a complete path
• mkdir -p proposal/january

66
Exercise 5-5 Create Directories

• The purpose of this exercise is to show you how
  to create directories

67
Delete Files and Directories

• Use rmdir to delete empty directories
• rmdir proposal
• Use rm to delete files and directories
• rm part
• To delete directories (even if not empty)
• rm r testdir
• You can use the two options in Table 5-17 with rm

User must have permission to delete file(s)
68
Exercise 5-6 Delete Files and Directories

• The purpose of this exercise is to show you how
  to delete files and directories on the command
  line
• When deleting files and directories, it is
  especially important to work only with the
  permissions necessary for the task and not as
  root, if possible
• As root, you can easily destroy your installation
  with the rm command, and there is no undelete in
  Linux
• Think twice before hitting enter on an rm command
  issued as root!

69
Link Files

• Each file is described by an inode
• To see the inode number you can enter ls I
• Each inode has a size of 128 bytes
• An inode contains all the information about the
  file besides the filename
• Link a reference to a file
• Create a hard link using ln, 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
• Create a symbolic link using ln s a symbolic
  link is assigned its own inode

70
Link Files (continued)
71
Link Files (continued)

• A symbolic link can point to a non-existing
  object if the object and its corresponding name
  no longer exist
• For example, if you erase the file old in the
  preceding example, in SLES 9 new will be shown in
  a different color in the output of ls, indicating
  that it points to a non-existent file
• An advantage of symbolic links is that you can
  create links to directories

72
Exercise 5-7 Link Files

• Links are very convenient in administration, as
  they help to avoid having different versions of
  the same file within the file system
• The purpose of this exercise is to learn how to
  set hard and symbolic links and know the
  difference between those two

73
Find Files

• In this objective you learn how to find files and
  programs using the following commands
• KFind
• find
• locate
• whereis
• which
• type command

74
KFind
75
KFind (continued)

• Table 5-18 shows the results of three different
  search strings

76
KFind (continued)
Use to narrow search
77
find
Usage find path criteria action
78
find (continued)

• You can use the option -exec to call up another
  command
• Examples
• find /usr/share/doc/ -name ".txt" -type f \
  /usr/share/doc/xine/faq/faq.txt
• find -mtime 0
• find -name letter -type f -exec grep \
  appointment \ -print appointment for \ next
  meeting 23.08.
• The two brackets are placeholders for the
  filenames that are found and passed to grep
• The semicolon closes the -exec instruction

79
locate

• locate is an alternative to find name
• The package findutils-locate must be installed
• find can be quite slow
• locate searches through a database previously
  created (/var/lib/locatedb), making it much
  faster
• The database is automatically created and updated
  daily by SLES 9
• Use updatedb to update it manually
• Examples
• locate letter_Miller
• locate umount

80
whereis

• whereis returns the binaries (option -b), manual
  pages (option -m), and the source code (option
  -s) of the specified command
• If no option is used, all this information is
  returned, if the information is available
• whereis is faster than find, but it is less
  thorough
• Example

81
which

• which searches all paths listed in the variable
  PATH for the specified command and returns the
  full path of the command
• It is especially useful if several versions of a
  command exist in different directories and you
  want to know which version is executed when
  entered without specifying a path

82
type command

• type command can be used to find out what kind of
  command is executed when command is entereda
  shell built-in command or an external command
• The option -a delivers all instances of a command
  bearing this name in the file system

83
Exercise 5-8 Find Files

• With about 100,000 files in a usual installation,
  it is essential to be able to find files
  effectively within the file system
• It is possible to search using part of the file
  name, but also to look for files that contain a
  certain string, as covered in the exercise after
  this one
• In this exercise you practice finding files and
  directories

84
Search File Content

• Suppose you have dozens of text files and you
  need to find all files that include a particular
  word, phrase, or item
• To scan these files without opening them in an
  editor, you need to know the following
• How to Use the Command grep
• How to Use Regular Expressions

85
How to Use the Command grep

• grep search_pattern filename
• If you specify several files, the output will
  print the matching line and the corresponding
  filenames
• grep "(bB)lurb" file
• For more complex patterns, use egrep (or grep
  -E), which accepts extended regular expressions
• Should comply with the standard regex syntax

86
How to Use the Command grep (continued)
87
How to Use Regular Expressions
88
Exercise 5-9 Search File Content

• Sometimes all you know is a string that appears
  within a certain file, but you do not know in
  which file exactly
• The purpose of this exercise is to show you how
  to find such a file

89
Archive, Back up, Compress, and Decompress Files

• In this objective, you learn how to
• Archive Files with ark
• Archive Files with tar
• Restore Files from tar Archives
• Copy Files to and from an Archive
• Use Data Backup Command-Line Tools
• Compress Files with gzip
• Decompress Files with gunzip
• Compress Files with bzip2
• Decompress Files with bunzip2
• View Compressed Files with zcat

90
Archive Files with ark

• The program ark lets you collect multiple files
  or even entire directories into an archive for
• Backing up data
• Preparing data to be sent via floppy disk or
  e-mail
• The standard file format for archives in Linux is
  .tar
• Tar files can be quite large, but you can
  compress them. ark archives and compresses in one
  step
• Formats supported .tar, .tar.gz, .tar.Z,
  .tar.bz2, .gz, .bz, .bz2, .lzo, .Z, .zip, .lzh,
  .zoo, .rar, .a

91
Archive Files with ark (continued)
92
Archive Files with tar

• tar is the most commonly used tool for data
  backup
• It requires an option, the name of the archive
  (or the device file) to be written to, and the
  name of the directory to back up
• tar -cvf /dev/st0 /home
• tar -cvf /backup/etc.tar /etc
• tar -czvf /backup/etc.tgz /etc
• tar -cvf /dev/st0 /home -X exclude.files
• tar -tvf /dev/st0
• find . -name ".txt" -type f -print0 tar \
  --null -cvf txt.tar -T -
• When an archive is created, absolute paths are by
  default made relative

93
Archive Files with tar (continued)
94
Restore Files from tar Archives

• tar -xvf /dev/st0
• Writes all files in the archive to the current
  directory
• Due to the relative path specifications in the
  archive, the directory structure of the archive
  is created here
• To extract the files to another directory, use
  the option -C, followed by the directory name
• If you want to extract just one file, you can
  specify the name of the file with the -C option
• tar -xvf /test1/backup.tar -C /home/user1/.bashrc

95
Exercise 5-10 Archive Files

• Files are frequently put into archives, as they
  can then be sent more easily as e-mail
  attachments
• Backups also often make use of archives
• Various tools exist for this purpose in Linux,
  and the purpose of this exercise is to show you
  the more common ones

96
Copy Files to and from an Archive

• cpio copies files into or out of a cpio or tar
  archive
• The archive can be another file on the disk, a
  magnetic tape, or a pipe
• In copy-out mode, cpio copies files into an
  archive
• find mystuff/ cpio -o gt mystuff.cpio
• In copy-in mode, cpio copies files out of an
  archive or lists the archive contents
• cat mystuff.cpio cpio -idvm
• In copy-pass mode, cpio copies files from one
  directory tree to another, combining the copy-out
  and copy-in steps without actually using an
  archive

97
Copy Files to and from an Archive (continued)
98
Use Data Backup Command-Line Tools

• rsync creates copies of complete directories
  across a network to a different computer
• -a option switches rsync to archive mode
• rsync -a /home /shadow
• /. at the end of the directory to be mirrored
  indicates that this directory is not included in
  the copy
• dd used to convert and copy files byte-wise
• dd if/etc/protocols ofprotocols.org
• mt lets you work with magnetic tapes
• mt -f /dev/st0 status

99
Use Data Backup Command-Line Tools (continued)

• Use cron to automate backup (command line)
• System jobs are controlled by the file
  /etc/crontab and the files in /etc/cron.d/
• Other jobs are defined by the scripts in
  /etc/cron.hourly/, /etc/cron.daily/,
  /etc/cron.weekly/, and /etc/cron.monthly/
• You specify which users can create cron jobs in
  /var/spool/cron/allow and /var/spool/cron/deny
• By default, only root can define jobs
• Users can edit their own crontab files by
  entering crontab -e

100
Compress Files with gzip

• gzip options file
• gzip .tex
• gzip -c price_list gt price_list_backup.gz

101
Compress Files with gzip (continued)
102
Decompress Files with gunzip

• gunzip decompresses a file compressed with gzip
  and removes the suffix .gz
• This function corresponds to the command
• gzip -d file
• The syntax for the command gunzip is
• gunzip file.gz
• Combining tar and gzip has been covered under
  Archive Files with tar

103
Compress Files with bzip2

• bzip2 options file
• bzip2 generates files twenty to thirty percent
  smaller than gzip, but they take longer to
  compress
• tar -cjvf /backup/etc.tar.bz2 /etc

104
Compress Files with bzip2 (continued)
105
Decompress Files with bunzip2

• bunzip2 decompresses files compressed with bzip2
  and removes the suffix bz2
• Equivalent to bzip2 -d file
• bunzip2 file.bz2
• Examples
• tar -xjvf /backup/etc.tar.bz2
• bzip2 -d /backup/etc.tar.bz2 -c tar -xf -

106
View Compressed Files with zcat

• Use zcat to decompress files compressed with gzip
  and write them to the standard output
• The compressed file is not modified
• The function of zcat corresponds to
• gunzip -c -d
• The syntax for the command zcat is
• zcat file.gz

107
Exercise 5-11 Compress and Decompress Files with
gzip and bzip2

• Usually files are not just put into archives, but
  they are compressed as well to save on bandwidth
  and/or storage capacity
• In this exercise you practice compressing and
  decompressing files

108
Summary

• The Linux filesystem is arranged hierarchically
• There is only one root directory in Linux (/)
• Linux directories and files follow the FHS their
  locations can be described using absolute or
  relative pathnames
• /dev contains character and block-oriented device
  files used to identify most HW devices on the
  system
• /media and /mnt typically contain mount point
  subdirectories used to mount and access removable
  media

109
Summary (continued)

• Most system configuration files are stored under
  /etc shared libraries are stored under /lib
• /usr stores most system applications, whereas
  /opt stores most user applications
• Log files, spool directories, and
  application-specific files are typically stored
  under /var
• /boot contains information used to load the Linux
  kernel
• Home directories are typically located under /home

110
Summary (continued)

• /bin and /sbin contain executable binary programs
• /proc and /sys are virtual directories that
  contain information that is exposed by the Linux
  kernel
• The types of files the Linux filesystem are
  normal files, directories, linked files, device
  files, sockets, and named pipes
• You can use head, tail, cat, and less to view the
  contents of text files
• You can use cp, mv, rm, rmdir, and mkdir to
  create, change the location of, or remove files
  and directories

111
Summary (continued)

• Every file and directory has an inode
• Files may be a link to another file by name or by
  inode
• You may use KFind, find, locate, whereis, and
  which to find files
• Regular expression metacharacters can be used to
  specify certain patterns of text
• You can use ark, tar, and cpio to archive data
• You can schedule programs with cron
• Two common compression utilities are gzip and
  bzip2