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Book IX

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Directory and File Handling Commands

Without arguments, the ls command lists all the files in the current direc-

tory, like this:

$ pwd

/etc/mail

$ ls

access helpfile Makefile submit.cf virtusertable

access.db local-host-names sendmail.cf submit.cf.bak virtusertable.db

domaintable mailertable sendmail.mc submit.mc

domaintable.db mailertable.db statistics trusted-users

You can limit the display to certain files by typing a filename, which can

include wildcards. For example:

$ ls a*

access access.db

You can also specify the directory that you want to display, like this:

$ ls /etc/httpd

conf conf.d logs modules run

To display detailed information about the files in the directory, use the -l

switch, as in this example:

$ ls /etc/mail/s* -l

-rw-r--r-- 1 root root 57427 Jul 19 16:35 sendmail.cf

-rw-r--r-- 1 root root 5798 Feb 24 16:15 sendmail.mc

-rw------- 1 root root 628 Jul 24 17:21 statistics

-rw-r--r-- 1 root root 39028 Jul 19 17:28 submit.cf

-r--r--r-- 1 root root 39077 Feb 24 16:15 submit.cf.bak

-rw-r--r-- 1 root root 953 Feb 24 16:15 submit.mc

The cp command

The cp command copies files. Here’s the basic syntax:

cp [options] source-file destination-file

The following list describes the more important options for the ls command:

✦ -a: The same as -dpR.

✦ -b: Makes backup copies of existing files before they’re overwritten.

Sounds like a good plan to me.

✦ -d: Copies links rather than the files the links point to.

✦ -f: Removes files that will be overwritten.

✦ -i: Interactively prompts for each file to be overwritten.

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✦ -l: Creates links to files rather than actually copying file contents.

✦ -p: Preserves ownership and permissions.

✦ -R: Copies the contents of subdirectories recursively.

✦ -s: Creates symbolic links to files rather than actually copying file

contents.

✦ -u: Replaces destination files only if the source file is newer.

To make a copy of a file within the same directory, use cp like this:

$ cp sendmail.cf sendmail.cf.backup

If you want to copy a file to another directory without changing the filename,

use cp like this:

$ cp sendmail.cf /home/doug

You can use wildcards to copy multiple files:

$ cp send* /home/doug

To include files in subdirectories of the source file, use the -R switch, like

this:

$ cp –R /etc/*.cf /home/doug

In this example, all files in the /etc directory or any of its subdirectories

that end with .cf are copied to /home/doug.

The rm command

The rm command deletes files. The syntax is as follows:

rm [options] file

The options are described in the following paragraphs:

✦ -f: Removes files that will be overwritten.

✦ -i: Interactively prompts for each file to be overwritten.

✦ -R: Copies the contents of subdirectories recursively.

To delete a single file, use it like this:

$ rm any.old.file

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To delete multiple files, use a wildcard:

$ rm any.*

To delete an entire directory, use the -r switch:

$ rm –r /doug/old.files

The mv command

The mv command moves files or renames them. In Linux, moving and renam-

ing a file is essentially the same thing. Moving a file changes the file’s direc-

tory location but leaves its name the same. Renaming a file leaves the file in

the same directory but changes the file’s name.

The syntax of the mv command is

mvp [options] source-file destination

The following paragraphs describe the options:

✦ -b: Makes backup copies of existing files before they’re overwritten.

Sounds like a good plan to me.

✦ -f: Removes files that will be overwritten.

✦ -i: Interactively prompts for each file to be overwritten.

✦ -u: Replaces destination files only if the source file is newer.

To move a file to another directory, provide a filename for the first argument

and a directory for the second, like this:

$ mv monthly.report /home/Debbie/

To rename a file, provide filenames for both arguments:

$ mv monthly.report august.monthly.report

The touch command

The touch command is one of the more interesting Linux file management

commands. Here’s the syntax:

touch [options] file

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Here are some of the options that you can use:

✦ -a: Changes the access time only.

✦ -c: Doesn’t create files that don’t exist.

✦ -m: Changes the modification time only.

The basic form of the touch command looks like this:

$ touch monthly.report

If you use touch on an existing file, the touch command changes the modi-

fication date of the file. If you use it on a command that doesn’t exist, the

touch command creates a new, empty file.

The cat command

The cat command displays the contents of a file. It has the following syntax:

cat [options] [filename...]

Notice that the filename is optional. If you omit the filename, the cat com-

mand obtains its input from the console, which you can redirect if you want.

Also notice that you can specify more than one filename. If you do, the files

are combined to create a single output stream.

Here are some of the options you can use:

✦ -A: Displays new line characters as $, tab characters as ^I, and control

characters with a caret (^).

✦ -b: Numbers all nonblank lines as they’re displayed.

✦ -e: Displays new line characters as $ and control characters with a

caret (^).

✦ -E: Displays new line characters as $.

✦ -n: Numbers lines as they are displayed.

✦ -s: Squeezes multiple spaces down to a single space.

✦ -t: Displays tab characters as ^I and control characters with a caret

(^).

✦ -T: Displays tab characters as ^I.

✦ -v: Shows nonprinting control characters with a caret (^).

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Commands for Working with Packages and Services

Here’s a basic example:

$ cat /etc/hosts

# Do not remove the following line, or various programs

# that require network functionality will fail.

127.0.0.1 LSERVER localhost.localdomain localhost

If you don’t provide any filename arguments, the cat command copies text

from the keyboard and displays it on the console. You can use the cat com-

mand along with output redirection to quickly create a short text file, like

this:

$ cat >mytext

This is line one.

This is line two.

This is line three.

<ctrl+D>

For the last line, press Ctrl+D. This signals the end of the input to the cat

command.

Commands for Working with Packages and Services

As a Linux administrator, you frequently need to start and stop services and

check the status of installed packages or install new packages. The following

sections describe the Linux commands that help you to perform these tasks.

The service command

You use the service command to check the status of services and to start,

stop, or restart services. You need to restart a service whenever you make

a configuration change in order for your changes to take effect. Here’s the

basic syntax:

service [service] [ start | stop | restart ]

The following paragraphs describe some typical uses of the service

command:

✦ To check the status of the httpd service (Apache), use this command:

$ service httpd status

✦ To stop the httpd service:

$ service httpd stop

✦ To start the httpd service:

$ service httpd start

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✦ To restart the httpd service:

$ service httpd restart

The only trick to using the service command is that you have to know the

name of the service. If you’re not sure of the name, you can run the service

command to display the status of all services, like this:

$ service --status-all

It will take a few moments to list all the services, but after the command is

done, you can scroll through the list to find the service that you’re looking

for.

Table 9-3 lists some of the more common services.

Table 9-3 Common Linux Services

Service Description

atd Runs commands scheduled by the at command.

autof

Automatically mounts file systems.

crond

Runs programs at specified times.

dhcpd

The DHCP server.

finger The Internet finger service.

httpd

The Apache Web server.

imap

The IMAP mail protocol.

imaps

Secure IMAP service (SSL).

ipop3

The POP3 mail protocol.

iptables

Automatic packet filtering for firewalls.

isdn

ISDN services.

named

The Bind DNS server.

netf

The network file system.

network

Activates and deactivates all network interfaces.

nfs

Native Unix/Linux network file sharing.

pop3s

Secure POP3 service (SSL).

sendmail

The Sendmail service.

smb

The Samba file and printer sharing service.

snmpd

Simple Network Management Protocol.

telnet

The Telnet server.

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The rpm command

The rpm command is the Red Hat Package Manager, a tool that simplifies

the task of managing packages on your Linux system. Although rpm was

originally developed for Red Hat Linux, it’s now found on many Linux distri-

butions, including Fedora (which is, of course, based on the Red Hat

distribution).

Here’s the basic syntax for querying the status of a package:

rpm -q [options] package

To install, upgrade, or remove a package, the basic syntax is more like this:

rpm [ -i | -u | -e ] [options] package-file

You can use quite a few options with the rpm command, but the most

common are

✦ -v: Displays verbose output. You may as well know what rpm is doing

while it chugs along.

✦ -h: Displays hash marks (#) periodically to reassure you that the pro-

gram hasn’t died.

You can use rpm to determine the status of installed packages on your

system by using the -q switch. For example, to find out what version of

Sendmail is installed, use this command:

$ rpm -q send*

Sendmail-8.12.8-4

Notice that you can use a wildcard with the package name. If you don’t have

a package whose name matches the package name you supply, you get the

message package not installed.

To install a package, you use the -i switch and specify a wildcard filename

that indicates the location of the package file. It’s also a good idea to use

the -v and -h switches. For example, to install Sendmail from a mounted

CD-ROM drive, you use this command:

$ rpm –ivh /mnt/cdrom/Fedora/Packages/sendmail*

If you want to update to a newer version of a package, you can use the -u

switch instead of the -i switch:

$ rpm –uvh /mnt/cdrom/Fedora/Packages/sendmail*

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Finally, you can remove a package by using the -e switch:

$ rpm –e send*

Note that to use the rpm command, you should log on as root.

Commands for Administering Users

The following sections describe the Linux commands that you can use to

create and manage user accounts from a command shell.

You should log on as root to perform these tasks.

The useradd command

The useradd command creates a user account. Here’s the basic syntax for

adding a new user:

useradd [options] user-name

You can also use this command to change the default options for new users.

In that case, the syntax is more like this:

useradd -D [options]

The options are as follows:

✦ -c comment: Typically, the comment is the user’s full name.

✦ -d home-dir: The home directory of the new user.

✦ -e date: The expiration date for the user.

✦ -f time: The number of days between logons before the user is consid-

ered expired.

✦ -g group: The initial logon group for the user.

✦ -G groups: Additional groups the user should belong to.

✦ -m: Creates the new user’s home directory if it doesn’t exist already.

✦ -s shell-path: Specifies the user’s logon shell.

The following option is valid only with -D:

✦ -b base-dir: Provides the default base directory if a home directory is

not specified.

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Its most basic form, the useradd command, creates a user with default

option settings:

$ useradd theodore

This command creates a user named theodore.

Here’s a command that specifies the user’s full name in the comment option:

$ useradd -c ‘Theodore Cleaver’ theodore

The following command creates a temporary account named ghost that

expires on Halloween 2012:

$ useradd -e 2012-10-31 ghost

If you want to see what the default values are for account options, use the -D

option without any other parameters:

$ useradd -D

GROUP=100

HOME=/home

INACTIVE=-1

EXPIRE=

SHELL=/bin/bash

SKEL=/etc/skel

The usermod command

The usermod command modifies an existing user. It has the following

syntax:

usermod [options] user-name

The options are as follows:

✦ c comment: Typically, the comment is the user’s full name.

✦ -d home-dir: The home directory of the new user.

✦ -e date: The expiration date for a logon.

✦ -f time: The number of days between logons before the user is consid-

ered expired.

✦ -g group: The initial logon group for the user.

✦ -G groups: Additional groups the user should belong to.

✦ -m: Creates the new user’s home directory if it doesn’t exist already.

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✦ -s shell-path: Specifies the user’s logon shell.

✦ -l: Locks an account.

✦ -u: Unlocks an account.

Here’s an example that changes a user’s full name:

$ usermod -c ‘The Beave’ theodore

The userdel command

The userdel command deletes a user. It has a simple syntax:

userdel [-r] user-name

If you specify -r, the user’s home directory is deleted along with the

account.

The chage command

The chage command modifies date policies for a user’s passwords. It has

the following syntax:

chage [options] user-name

The following paragraphs describe the options you can use:

✦ -m days: Specifies the minimum number of days allowed between pass-

word changes.

✦ -M days: Specifies the maximum number of days allowed between pass-

word changes.

✦ -d date: The date of the last password change.

✦ -E date: The date on which the account will expire.

✦ -W days: The number of days prior to the password expiring that the

user will be warned the password is about to expire.

✦ -I days: The number of days of inactivity after the password has

expired that the account is locked out. Specify 0 to disable this feature.

Here’s an example that sets an account to expire on Halloween 2016:

$ chage -E 2016-10-31 ghost

If you specify a username but no other options, you’re prompted to enter

each option. This is a lot easier than trying to remember all the switches!

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