Sed – An Introduction and Tutorial

Bruce Barnett

Last update: Wed Apr 16 20:55:07 EDT 2008
Thanks to Keelan Evans, Fredrik Nilsson, and Kurt McKee for spotting some typos.
Thanks to Wim Stolker and Jose' Sebrosa as well.
Thanks to Olivier Mengue.
Thanks to Andrew M. Goth.
Thanks to David P. Brown.

You are allowed to print copies of this tutorial for your personal use, and link to this page, but you are not allowed to make electronic copies, or redistribute this tutorial in any form without permission.

admin July 15, 2008linux, sedNo Comments

find linux

real world unix/linux FIND usage

find . -type f -size +10000 -exec ls -al {} \;
find . -atime +1 -type f -exec mv {} TMP \; # mv files older then 1 day to dir TMP
find . -name "-F" -exec rm {} \; # a script error created a file called -F
find . -exec grep -i "vds admin" {} \;
find . \! -name "*.Z" -exec compress -f {} \;
find . -type f \! -name "*.Z" \! -name ".comment" -print | tee -a /tmp/list
find . -name *.ini
find . -exec chmod 775 {} \;
find . -user xuser1 -exec chown -R user2 {} \;
find . -name ebtcom*
find . -name mkbook
find . -exec grep PW0 {} \;
find . -exec grep -i "pw0" {} \;
find . -atime +6
find . -atime +6 -exec ll | more
find . -atime +6 -exec ll | more \;
find . -atime +6 -exec ll \;
find . -atime +6 -exec ls \;
find . -atime +30 -exec ls \;
find . -atime +30 -exec ls \; | wc -l
find . -name auth*
find . -exec grep -i plotme10 {};
find . -exec grep -i plotme10 {} \;
find . -ls -exec grep 'PLOT_FORMAT 22' {} \;

admin July 10, 2008find, linuxNo Comments

process unix

Monitoring and Tracing Unix Processes

Overview This article is intended for use by any Unix/DBA Administrator who needs to monitor trace information from a UNIX process. For a more detailed look at the "truss" command using Sun Solaris, check out: (Using the "truss" command in Solaris) How to Trace Unix System Calls for a Process…

admin July 10, 2008process, unixNo Comments

linux unix

Timing Read and Write Functions in UNIX

The following syntax can be used to time how well write activities are occuring on a set of file systems (drives). In this test, I will create a 1GB file and time it: [bash highlight="1"] # time dd if=/dev/zero of=/u03/test/large_file.dat ibs=1024 count=1048576 1048576+0 records in 2097152+0 records out real 0m33.086s…

admin July 10, 2008linux, read, timing, unix, writeNo Comments

filesystem linux

How-To Make the root filesystem read-only

Introduction

There are several reasons why you might want to make your root file system read only. I wanted to have a system on a flash disk, and since flash disks are damaged after repeated read-write circles the read-only root is a very nice solution. Other reasons why you would want to make your root partition read only include:

If you want maximum security for your server, and want it to boot from a read only medium (i.e. a CD-ROM)
If you want to make your own live-cd
To avoid that power loss or system crash damage the root partition.
If you want to mount the same nfsroot on several thin clients

The following procedure is what i did to turn my SuSE 10.1 root file system to read-only. It should work on both earlier and later versions but i haven’t tested it yet. There could be better/more elegant solutions, if you think that something is missing please fill free to edit this howto.

Acknowledgments

Some of the information on this howto where found here.

admin July 9, 2008filesystem, linux5

linux tar

Moving Directories using TAR

The following can be used to move a directory/sub-directory when the directory is the entire mount point: [bash]# dump 0f - /dev/rdsk/c207d0s0 | restore rf -[/bash] NOTE: Must be in the target directory! The following can be used when the directory to be moved is a sub-directory to the mount…

admin July 9, 2008linux, tarNo Comments

find linux

Using the find Command

Overview This document provides several examples of using the find command in a UNIX environment. Finding Groups with Numeric Values [bash]# find /db? -group 15 | xargs chgrp[/bash] Often a user or system administrator will encounter directories that have a numeric value. This is an indication a change user made…

admin July 9, 2008find, linuxNo Comments

filesystem linux

The /proc Filesystem

One of the ways in determining what is going on inside the UNIX kernel is to make use of the /proc filesystem. Some of that information may be disk arrays connected to your server or querying kernel parameters. The /proc filesystem offers an interface to important kernel data structures that provide information about the state of a running UNIX kernel by use of special files. The System Administrators uses the UNIX cat command to list the contents of those special files.

Under Linux, it is also possible to set certain kernel parameters by using the echo command. For example, to change the kernel parameter value used to control the maximum socket receive buffer size, net.core.rmem_default, to 262144, use the following:

# echo 262144 > /proc/sys/net/core/rmem_default

It is important to understand when setting kernel parameters in Linux using the echo command, (as in the above example), these settings need to be applied each time the system boots. Some distributions of Linux already have a setup method for this during boot. On Red Hat, this can be configured in /etc/sysctl.conf: (like: net.core.rmem_default = 262144).

This article attempts to list some of the more common files used by System Administrators. Although most of these special files are general enough to apply to all flavors or UNIX (Solaris, Linux, HP-UX, etc.), I indicate those that only apply to a particular platform.

admin July 9, 2008filesystem, linuxNo Comments

linux man

Redirecting MAN Pages to a File

Trying to redirect a man page to a file using only the redirection command will produce many unreadable characters. Before redirecting the file, pipe the man page through the "col" command as show below. [bash]# man rcs | col -bx > rcs.txt[/bash]

admin July 9, 2008linux, manNo Comments

filesystem linux

Troubleshooting the “device is busy” Error Attempting to umount a Disk

Before attempting to dismount a filesystem, it must be inactive. If “any user” has one of the filesystem’s directories as their current directory or has any file within the filesystem open, you will receive an error message, like the one below, when attempting to unmount the filesystem:

# umount /dev/dsk/c0t2d0s7
umount: /dev/dsk/c0t2d0s7: device is busy

Well, the fuser command to the rescue. The fuser command may be used to determine which files or directories within a filesystem are currently in use and to identify the processes and users that are using them.

admin July 9, 2008filesystem, fuser, linuxNo Comments