A Guide to Unix Using Linux Fourth Edition

A Guide to Unix Using Linux Fourth Edition

Chapter 8Exploring the UNIX/Linux Utilities

A Guide to Unix Using Linux, Fourth Edition 2

Objectives

• Understand many of the UNIX/Linux utilities that are available and how they are classified

• Use the dd utility to copy and convert files

• Monitor hard disk usage

• Use system status utilities

• Monitor and manage processes

• Check the spelling of text in a document


Objectives (continued)

• Use the cmp command to compare the contents of two files

• Format text to create and use a man page

• Use the dump command to back up a system

• Send and receive e-mail

• Use basic network commands and utilities


Understanding UNIX/Linux Utilities

• UNIX/Linux utilities are classified into:– File processing– System status– Networking– Communications– Security– Programming– Source code management– Miscellaneous


Classifying UNIX/Linux Utilities

• Several categories– Network tasks– Programming tasks– File-processing utilities

• Make up the largest category

• Display and manipulate files




Classifying UNIX/Linux Utilities (continued)










Using the dd Command


Checking Hard Disk Usage

• Basic strategies used to maintain adequate free space:– Be vigilant against running dangerously low on free

space• Use df command

– Watch for conspicuous consumption• Use du command

– Follow a routine schedule for “garbage” collection and removal

• Use a combination of find and rm commands


Using the df Utility

• If entered without specifying file system, shows information for all mounted file systems


Using the df Utility (continued)


Using the du Utility

• With no options, report is based on all file usage– Starts at current directory – By default, output is in number of 512-byte blocks



Removing Garbage Files

• Garbage files are temporary files that lose their usefulness after several days– Remove to free space– Example: core files, compilation output

• Core file: created when executing program attempts to do something illegal– Example: accessing another user’s memory

• Use find and rm to find and remove garbage files:find . "(" -name a.out -o -name core ")" -exec rm {} \;


Using System Status Utilities

• System status commands reflect system’s performance

• You can redirect the output of these commands to a file– File can later be:

• Printed

• Forwarded to system administrator and system tune-up specialists


Using the top Command


Using the uptime Command

• Example: use it to track how long system has been up since last problem requiring a reboot


Using the free Command

• Swap space is disk space that acts like an extension of memory


Using the free Command (continued)


Forwarding top and free Output

• You may forward output of top and free to a computer support person for analysis– Example:

top n 3 > topdata

lpr topdata


Managing Processes

• When you run a program, it starts one or more processes– Processes are identified through a unique number

• Process id or PID

• UNIX and Linux offer utilities to:– Manage how a program is run– Monitor processes– Kill processes


Running Processes in the Background

• UNIX/Linux is a multitasking OS– You can run processes in the background

• To run a process in background:– Append the & character

• Example:top&


Monitoring Processes

• If used with no options, shows a list of processes associated with the current login session


Monitoring Processes (continued)


Killing Processes

• System administrator may want to kill a user’s process because:– Associated program is malfunctioning– Associated program is using too many system

resources• A user may want to kill a process that is running in

the background


Checking the Spelling of a Document

• ispell– Scans a text document– Displays errors on screen– Suggests other words with similar spellings as

replacements for unrecognized words


Checking the Spelling of a Document (continued)


Comparing Files

• If the contents are identical, there is no output

• Otherwise, output specifies first byte (character) that is different between the files


Formatting Text in UNIX/Linux


Archiving and Backing Up Files

• Good practice to periodically archive or back up files

• You can back up files to:– CD, DVD, tape, or another removable medium

• For backup to CD/DVD, consider using a GUI tool– Example: GNOME CD/DVD Creator GUI software

• Part of Nautilus


Using the dump Command


Using the restore Command

• Restores from a backup medium created via dump – By default, copies back to current working directory

• Example: restore -r -f /dev/st0


Using mail to Send Mail

• Press Ctrl+d to exit the text mode

• To leave the mail utility, type q and press Enter


Using mail to Send Mail (continued)


Using mail to Send Mail (continued)


Using Networking Utilities

• UNIX and Linux offer many utilities to accommodate a connection to the network– ifconfig– ping– traceroute– netstat


Using the ifconfig Utility

• Internet Protocol (IP) is used to help ensure that information on a network goes to the right place– IP address uses a dotted decimal notation

• Consists of four octets separated by periods

• Identifies a computer/device and the network it is on


Using the ping Utility

• Examples:– ping [email protected]– ping redhat.com

mailto:[email protected]


Using the traceroute Utility

• Sample use:– To ensure your computer is connected and working– To ensure your network is working from point to

point


Using the netstat Utility

• Information provided by netstat includes:– Network protocol communications– Network connections established by host computer– Network routing information– Information about remotely logged computers


Sharing Resources Using Network File System

• Network File System (NFS): used for resource sharing over a network– Once partition is mounted, access is transparent

• mount bluefin:/home/mpalmer/shared /mnt/shared

– Three versions typically supported:• NFSv2, NFSv3, and NFSv4

– Client and host communicate via RPCs• RPC: Remote Procedure Call

• Portmap service:– Handles RPC request to mount a partition– Makes computer act like a server for NFS file access


Sharing Resources Using Network File System (continued)

• To start a service, use service command– service portmap

• NFS security handled through entries in:– /etc/hosts.allow, /etc/hosts.deny, and /etc/exports

/home/mpalmer/shared 192.168.0.72(ro) 192.168.0.84(ro)/home/mpalmer/docs 192.168.0.72(rw) 192.168.0.41(rw)


Accessing Microsoft Windows Systems Through Samba

• Samba: utility that uses the SMB protocol– Server Message Block (SMB) is used by Windows

systems for sharing folders and printers

• Typical configuration file:– /etc/samba/smb.conf file

• Some ways to access Windows shared drives:– Network Servers Windows Network– Computer More Applications Network Servers

File Browser Windows Network– K menu KNOPPIX Utilities Samba Network

Neighborhood


Summary

• Some useful utility programs are:– dd, df, and du for converting files, checking free space,

and checking disk usage, respectively– find and rm can be used together to remove garbage

files– top and free provide detailed views of system internals– uptime shows how long a system has been up– ps and kill to display and kill processes– ispell to check for spelling errors in a file– nroff, troff, and groff for formatting output


Summary (continued)

• Other useful utility programs are:– dump and restore to archive and restore backups– mail to send and retrieve mail– ifconfig, ping, traceroute, and netstat for viewing

information about the network connection and for troubleshooting the connection

• Services for sharing resources over network:– Network File System (NFS) to access resources in

another UNIX/Linux computer– Samba to access resources in a Windows computer


Command Summary

Documents

A Guide to Unix Using Linux Fourth Edition