chapter 4: understanding users and file systems

8/14/2019 Chapter 4: Understanding Users and File Systems

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Chapter 4:

Understanding Users and FileSystems

The Complete Guide to Linux System

Administration


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The Complete Guide to Linux System Administration 2

Objectives

Create and manage user and group accounts

View and set access permissions on files and

directories Understand how file systems are configured and

accessed

Perform basic file compression and archiving

tasks


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Linux Users and Groups

Must first log in using valid user account name

and password

More user accounts on Linux system More work required to keep them running

smoothly


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Types of User Accounts

(continued)


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(continued)

su command

Temporarily changes access rights to those of

another user Without any parameters

Change to root account

Hyphen after su command

Causes command to run login scripts Places you in login directory of user


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(continued)

Preconfigured user accounts

Regular user accounts

Users who log in at keyboard and use Linux system Commonly associated with named individuals

Special user account

Used by Linux programs

Created during installation of Linux Vary depending on services installed


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Linux Groups

Group

Collection of user accounts

Can be collectively granted access to files anddirectories

Each user in Linux is assigned to primary group

/etc/group file

Lists members of each defined group


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Linux Groups (continued)


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User and Group Files /etc/passwd

Stores user account information

Password information not stored in this file

Contents include: User account name

Password

User ID number (UID)

Group ID number (GID)

Users real name

Home directory

Default shell


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User and Group Files (continued)

/etc/group file

Defines groups on Linux system

vigr command Edit this file

Contents include:

Name of group

Group password GID number

Members of group


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Shadow Passwords

/etc/shadow

Stores encrypted passwords

Can only be read by: Root user

Certain utilities

Shadow password suite

Collection of password-related programs Have been modified to recognize /etc/shadow file


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Changing User Passwords

Can change password of any user account on

system

When logged in as root Use passwd command

Standard procedure

System administrator assigns initial password to

new account User immediately selects new password


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(continued)

To change users password

Use passwd without any parameters

Must enter current password


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(continued)

Good password characteristics

At least five characters long

Include digits or punctuation marks Mix uppercase and lowercase letters

Easy for account owner to remember

Hard for anyone else to guess

Not created from simple manipulation of: Word found in dictionary

Name of person or place


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User Information Commands

id command

Shows effective UID

logname command View user name that you used to log in

whoami command

Shows user name of currently effective UID

groups command

Lists all groups you are a member of


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User Information Commands

(continued)

who command

Lists all regular users on system

Shows location where they are logged in

w command

Information from who command, plus:

Time person logged in

Program they are running Information about system resources user is

consuming


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File Permissions

Files and directories have

Owner

Group

Linux determines who can access file or directory

based on:

Who owner is

Which group is assigned to object File permissions define access granted to file or

directory


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File Permissions (continued) Access mode

Permissions

Read permission (r) Write permission (w)

Execute permission (x)

Permissions can be assigned by:

User permissions Group permissions

Other permissions


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File Permissions (continued)


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Changing Ownership chown command

Change user and group assigned to file ordirectory

Can only use when logged in as root Example: chown jtaylorManagers report.doc

Can use graphical file manager to change ownerof file

chgrp command Change group assigned to file or directory

Example: chgrp managers report.doc


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Changing File Permissions

chmod (change mode) command

Change file permissions

Regular users can alter permissions assigned toany file or directory that you own

Example: chmod o+w reportDoc

System administrators normally use shortcut

syntax


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(continued)

Alternate syntax

Each of sets of three permissions is represented

by number from 0 to 7 Example: chmod 640 report.doc

Graphical environment provides easy method of

setting file permissions

Properties dialog box Permissions tab


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(continued)


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(continued)


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Default File Permissions

rw-rw-rw-

umask command

Defines mask to stop certain permissions frombeing granted by default when files created

Executed automatically when you log in to Linux

Uses same three-digit permission codes as chmod

command


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Introducing the File System

Managing file system is basic task for system

administrators


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Partitions and File Systems

Partition

Distinct area of hard disk

Has been prepared to store particular type of data File system

Arrangement of information on device such as

hard disk

df command See status of all currently accessible file systems


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Partitions and File Systems

(continued)


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Inodes and Links inode

Hold information about files

Within ext2 or ext3 file system

Has associated number

Controls file to which it points

Does not contain file name

File record contains:

File name

Inode number for file


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Inodes and Links (continued) Directory record contains list of files with

corresponding inode numbers

Link allows two or more file records to refer to

same physical data stored in file system Symbolic link

File that refers to another file or directory, ratherthan containing data itself

Used when same data must be accessed from twolocations in directory structure

Takes only a few bytes of hard disk space


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Inodes and Links (continued) ln command

Create symbolic link

Use -s option

Syntax: ln -s

Hard link

File record that includes file name and inode

Just like regular file record Refers to inode that already has file record

pointing to it


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Inodes and Links (continued)


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Inodes and Links (continued)


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File Types

Different types of files are used to perform

different functions

Stat command Ties together file name with inode

Shows information about inode


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File Types (continued)


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Accessing Removable Media To use any file system

Must be mounted

Mount command Instruct Linux how to access file system

Mount point

Path in directory structure where you access data

in file system

umount command

unmount media


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Accessing Removable Media

(continued)

fdformat command

Format 3.5-inch disk

/dev/fd0 Device name for 3.5-inch disk drive


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Using find

find command

Helps find objects matching exact search criteria

Doesnt use prebuilt index Example: find /home -name "report.doc" -print


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Managing File Archives

System administrators often work with files that

include:

Compressed data Multiple files in archival format


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Compressing Files

Compressing files

Useful way to use less space for rarely accessed

data Makes files smaller before transmitting them over

network

gzip command

Compress any file gunzip command

Uncompresses file compressed using gzip


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Using tar and cpio

for Archiving Files

tar archive

Single file that can contain other files and directory

structure tar command

Create tar archive

Specify files to be included in backup archive on

command line Writes data to file name or device


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Using tar and cpio for Archiving

Files (continued)

cpio command

Copy in and out

Similar to tar Reads from STDIN channel for file names

Writes data back to STDOUT

tar and cpio

Help create incremental or multilevel backup


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Summary

User accounts form basis of file system security

in Linux

Can change user that you are working as Each user can belong to multiple Linux groups

Encrypted passwords are stored in

/etc/shadow file

Linux file security is controlled by ninepermissions


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Summary (continued) File systems

Organized collections of data

Created within partitions on hard disk

Hard and soft links

Refer to inode

Removable media must be mounted before it can

be accessed

Linux includes several utilities for compressing

files

chapter 4: understanding users and file systems

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