Tip 1 – Entering Control-Ms in vi

When you’re editing a text file in vi and the file was created in a Windows editor, you’ll see control-M (^M) characters at the end of each line.
If you want to add a new line and you want it to show up as a separate line in Windows, you’re going to have to add a control-M at the end of the line. The ^M is a single character, so you can’t just type ^ and then type M. You might think, given the name of the character, you could just hold down the Ctrl key and press m, but it’s not quite that simple.

What you need to do, in vi, is press Ctrl+v followed by Ctrl+m.

Tip 2 – Zipping files in UNIX

Usually when I’m working in UNIX and I want to compress a file, I use gzip:

gzip filename

This replaces the named file with a compressed version of it, with .gz added onto the end of the file name. To unzip the file do:

gunzip filename

This replaces the .gz file with the original file.

However, sometimes you need to create a .zip file. To do this use the zip command, but you need to know the syntax:

zip –r outputfile inputfile

For example:

zip –r temp.zip temp.txt

In fact you don’t need to specify the .zip file extension. If you give a file name without a file name extension, the .zip extension gets added automatically.

A new zip file is created and the original file is not deleted. To unzip just do:

unzip zipfile

This creates a new, unzipped file but does not delete the zip file.

I just tried this out and the following stats for compressing a small text file suggest that gzip is the more effective compression program:

temp.txt    677K
temp.txt.gz    416K
temp.zip    504K

Unfortunately, TortoiseCVS has no way to change the host names for modules you’ve already checked out. WinCVS can, supposedly, do this thanks to a macro. However, WinCVS stubbornly tells me I don’t have Python installed (I do) and therefore won’t let me use macros.

The solution is to just go through all the CVS “Root” files and change the host name. The Root file lives in the CVS directory at each level within a checked out module. This would be a laborious task by hand, but if you have SUA (Microsoft’s Subsystem for UNIX Applications) and Perl installed it’s easy. Just pull up a Korn shell and browse to the directory within which your checked out CVS modules live.

Run the following command.

find . -name 'Root' -print0 | xargs -0 perl -pi -e 's/oldhostname/newhostname/g'

For example, I ran the command:

find . -name 'Root' -print0 | xargs -0 perl -pi -e 's/cvshost/cvshost.mydomain.co.uk/g'

Which changed the Contents of the Root file from:

:pserver:achristie@cvshost:/company/repository

to:

:pserver:achristie@cvshost.mydomain.co.uk:/company/repository

To add a ^M in vi enter Ctrl+V followed by Ctrl+M.

I'm not sure what the problem was because the file the symlink was pointing to (wp-content/plugins/wp-cache/wp-cache-phase1.php) was still there. I had to use ClassicFTP to find this out because FileZilla doesn't show you were a symlink is pointing to. In fact, FileZilla treats symlinks as if they are directories and doesn't show the destination. ClassicFTP does, but doesn't show the ownership or permissions on files, which makes it inferior to FileZilla.

The other problem was that I couldn't simply delete it in FileZilla or ClassicFTP.

The solution I finally found was just to FTP to my Web server from the good old Windows command line. Fire up a command console window, type: ftp <host> then, when prompted, your user name and password. Use ls and cd to navigate to the directory containing the symlink.

Strangely, the symlink doesn't show up when you do an ls. However, if you do delete <symlink name> it will delete the symbolic link successfully.

Job done!

However, it's occasionally useful to have a Linux machine available to test something out, and great way to do this is to use a virtual machine. VMware would be your first choice if you want a virtual Linux machine, but, with a little effort, you can also use Microsoft Virtual PC.

Here's how to get Ubuntu on Virtual PC:

1. Download and install Virtual PC.
    
2. Download an Ubuntu Desktop Edition ISO. I downloaded 8.04 ("Hardy Heron").
     
3. Start Virtual PC, and create a new machine.
   
   (Video by Robert Cain: http://arcanecode.wordpress.com/)
     
   Note: Make sure to pick “Other” as the OS type.
   Give the machine 512 MB of RAM.
     
4. Start the new virtual machine.
     
5. When it starts up, go to the CD menu and choose Capture ISO image, pointing it at the desktop ISO you downloaded from Ubuntu. Capturing an image means the ISO file will show up like a CD in the virtual machine.
     
6. Ubuntu will start running from the CD image. When it starts, choose your language and then, at the next screen, press F4 to select an alternate starting mode.
   
     
7. When the menu pops up, change to Safe graphics mode and press Enter.
   There is a problem with the mouse not working in Virtual PC and this takes a little fiddling about to fix it. There is also an issue with sound (see the link at the bottom of this post for details about how to fix that - personally I didn't need sound, so I didn't bother trying to fix that).
     
8. Press F6.
    
9. Edit the command that is displayed, using the arrow keys to move the cursor to the end of the line and adding a space followed by “noreplace-paravirt” (without the quote marks) to the end of the command, then press Enter.
     
10. Leave the selected option as Try Ubuntu without any change to your computer.
    Note: do not choose the Install Ubuntu option.
      
11. After Ubuntu loads (note that at this point it's just running from the CD image, it's not installed on the virtual machine) double-click Install on the desktop.
    This runs the Ubuntu installer.
      
12. Follow through the installer. This part is very simple.
       
13. Once the install is done, go back into the CD menu (right-hand Alt key gets the mouse pointer out of the virtual machine) and release the ISO, otherwise when you reboot you'll go back to the installation menu.
      
14. Click the red button, top right of the Ubuntu desktop and shutdown the virtual machine.
    If it hangs at this point, don't worry about it.
      
15. Close the Virtual PC window and choose to shut down the machine.
     
16. Go into the Settings for the virtual machine.
    Robert Cain's video shows how to edit the Settings if you've never done this before:
    
     
17. Make sure Networking is set to the network adaptor that your PC is currently using.
    Note: if you want to be able to connect to/from the Ubuntu VM and your host PC, you need to use the Microsoft Loopback Adaptor. If this doesn't show up in the list of network adaptors you'll have to install it first. This is really easy. See http://support.microsoft.com/kb/839013, or this video from http://veedee-eyes.com
    
      
18. Save the Settings.
      
19. Start up the virtual machine again.
      
20. Once it gets to the "GRUB" line, press Esc.
    You should now see 3 entries to select from.
      
21. Leave Ubuntu 8.04, kernel 2.6.24-16-generic selected and press e.
      
22. On the next page, select the second entry that reads kernel /boot/vmlinuz… and press e again.
       
23. You will see a command line that ends with “xforcevesa”. Edit this, as before, adding a space followed by “noreplace-paravirt” (without the quotes) at the end of this line, then press Enter.
       
    You are now back at the previous selection screen with the entry kernel /boot/vmlinuz… still selected.
      
24. Press b and Ubuntu should boot correctly.
      
25. Once Ubuntu has loaded, open a terminal window (Applications > Accessories > Terminal) and on the command line enter:
       
    sudu nano /boot/grub/menu.lst
     
26. Enter your password and page down to near the bottom and locate “kernel /boot/vmlinuz…" in the “Ubuntu 8.04, kernel 2.6.24-16-generic” section.
      
27. Move the cursor to the end of the line after xforcevesa and add a space followed by “noreplace-paravirt” (no quotes).
      
28. Ctrl + O to write out.
      
29. Enter to accept the name.
     
30. Ctrl + X to close the file.
      
    Ubuntu should now be running inside Virtual PC.
      
31. Click the network icon in the upper right side of the Ubuntu toolbar:
     
      
32. Choose Wired Network.

That's it.

Now you can fire up an Ubuntu machine whenever you need it. And when you close it down, choose Save State and when you start it up again you'll be able to pick up exactly where you left off - for example, any programs that were running when you saved state will still be running when you start up the VM again in six months time.

I found the following site extremely helpful:

http://arcanecode.wordpress.com/2008/04/24/installing-ubuntu-804-under-microsoft-virtual-pc-2007/

If you get stuck, it's worth reading through all the comments on this page, which provide a lot of useful information.

perl banner.pl

Then create the following Perl script in your home directory and call it banner.pl.

# Perl script for printing banner showing name of local host use Text::Banner;
$a = Text::Banner->new;
$a->set(`hostname`);
$a->size(1);
$a->fill('');
$a->rotate('h'); print "\n";
drawlines();
print $a->get;
drawlines();
print "\n";
print "\n"; sub drawlines() {
    for ($loop=1; $loop<4; $loop++) {
        for ($n=1; $n<60; $n++) {
            print "=";
        }
        print "\n";
    }
}

Finally, install the Text::Banner perl module  from CPAN. Note: if you don't want to (or can't) install the Perl module in the normal way on the server, you can  download the zip file from the CPAN Web site (http://search.cpan.org/~lory/Text-Banner-1.00/Banner.pm), gunzip and tar xvf it  in your home directory and then change the 'use' statement to:use Banner::Banner;

If this file contains:
id:3:initdefault:
Fedora will boot into text-only mode.

If the file contains:
id:5:initdefault:
Fedora will boot into graphical mode.

X Sessions

1) Make sure you aren't being blocked by your firewall(s).

If you want to establish an X session from a machine on the internal network to a machine in your DMZ (e.g. your web server), you'll need to open up DMZ pinholes to allow the server in the DMZ to send screen data to ports 6000 (and, for some reason, 6001) on the Windows machine. If you're using Smoothwall you can do this quite easily in the Smoothwall admin pages.

For an X session, check that your firewall on the Windows machine isn't blocking traffic from port 6000 on the Windows machine to port 177 (XDMCP) on the server in the DMZ via the UDP protocol. If the firewall blocks this, the X manager on your Windows PC will not find the DMZ server even if its up and running and listening for connections on port 177.

2) Check gdm is running:

SSH to the server and enter the command:

ps -ef | grep gdm

This will tell you if gdm has been started.

3) If it's not running use the command:

gdm &

to start gdm

Be aware that gdm uses up a lot of processing power. If you have your server set up to boot up to run level 3 (text-only login), it will be sitting with a black screen and a login prompt. When you start gdm, this changes to a graphical login (although, of course, you won't see this if the server doesn't have a monitor). So when you've finished your remote X session, you should use the command:

gdm-stop

to stop gdm, switching the local display on the server back to the text-only login.

VNC

The main things for troubleshooting VNC are to check that you have SSHed into the server to open up the tunnel to port 590n (e.g. 5903 for display 3).

You should never allow direct VNC access to the server, only via a port forward tunnel opened by an SSH session. This means that your session info for the VNC client will be something like:

localhost:3

Which only works if port 5903 on the machine you're at has been forwarded to port 5903 on the server you've SSHed to.

If you HAVE SSHed to the server and you still don't get the authentication dialog box of your VNC client, check that vncserver is running on the server.

To do this use the command:

ps -ef | grep Xvnc

If there isn't an Xvnc process using display 3, start vncserver, telling it to use display number 3.

To do this, use the command:

vncserver :3

Just remember to stop vncserver after you close your VNC window:

vncserver -kill :3

Note: VNC may also be blocked by your firewall(s).

ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

It most likely means your MySQL is set up to authenticate logins and you didn't supply a user name and password. Try:

mysql -u root -p

Where root is the MySQL user (note: this is not a file system user account, even if it's got the same name as one). You will be prompted to enter the password.

If this still doesn't work, it probably means the user you're trying to log in as hasn't yet been added to MySQL's user database. To add a password for MySQL's root user do:

mysqladmin -u root password 'the-new-password'

NOTE:

If you forget a password you can do the following:
[Details from: www.idevelopernetwork.com/manual]

1) Stop MySQL by killing the mysqld process. The PID for this process is stored in the mysqld.pid file in the mysqld database directory, so you can stop the process by doing this (as root):

kill `cat /var/run/mysqld/mysqld.pid`

2) Restart mysqld with the --skip-grant-tables option.

3) Set a new password with the mysqladmin password command:

mysqladmin -u root password 'the-new-password'

4) Now you can either stop mysqld and restart it normally, or just load the privilege tables with:

mysqladmin -h hostname flush-privileges

5) After this, you should be able to connect using the new password.

However, I tried so many things, I'm not entirely sure what sorted it. I suspect it was installing tomcat5-webapps. I ran the following commands:

yum install tomcat5
yum install tomcat5-webapps
yum install tomcat5-admin-webapps

Note: yum install tomcat5 did nothing useful because Fedora Core 5 comes with Tomcat 5 and I'd done a complete yum update after installing FC5.

One of the other things I did yesterday was to add the following lines in /etc/httpd/conf/httpd.conf:

LoadModule proxy_ajp_module modules/mod_proxy_ajp.so
ProxyRequests Off

# transfer URLs for 'hs'
ProxyPass /hs/ http://localhost.localdomain:8080/hs/
ProxyPassReverse /hs/ http://localhost.localdomain:8080/hs/

I then restarted httpd.
And finally, since yesterday, I did a
shutdown -r now

This morning, I browsed to http://localhost:8080 in a browser on the Linux machine and Tomcat works.

I then opened up port 8080 in the firewall, so that I can see the Tomcat home page from other machines on the network by browsing to http://:8080.

So, at last, I've got Tomcat working. Now for Alfresco.

1) On the PC, configure and save a PuTTY session with a tunnel from port 5903 on the local host to port 5903 on the remote (Linux) machine.

2) Use this PuTTY session to connect to the Linux machine.

3) Log in as root.

4) If you haven't already done so, change the desktop VNC uses from the default twm to either Gnome or KDE by editing your xstartup file:

a) vi ~/.vnc/xstartup

b) For KDE, replace "twm &" with "startkde &".
For Gnome, replace "twm &" with "exec gnome-session &".

c) Enter vncserver :3
This launches the VNC server and tells it to use display 3.
(The first time you do this you'll be asked to supply a password.)

5) On the PC, start you VNC client (e.g. TightVNC - Fast Compression).

6) VNC to localhost::5903

7) Enter the password you supplied to vncserver.

You're in.

8) When you're finished, turn off vncserver (for security) by entering:

vncserver -kill :3

The problem appears to be with the httpd.conf file (/etc/httpd/conf/httpd.conf). This file contains a large set of LoadModule commands. Seems like these are wrong by default.

To correct this, back up the existing file and replace these commands with the following:

LoadModule auth_basic_module modules/mod_auth_basic.so
LoadModule auth_digest_module modules/mod_auth_digest.so
LoadModule authn_file_module modules/mod_authn_file.so
LoadModule authn_alias_module modules/mod_authn_alias.so
LoadModule authn_anon_module modules/mod_authn_anon.so
LoadModule authn_dbm_module modules/mod_authn_dbm.so
LoadModule authn_default_module modules/mod_authn_default.so
LoadModule authz_host_module modules/mod_authz_host.so
LoadModule authz_user_module modules/mod_authz_user.so
LoadModule authz_owner_module modules/mod_authz_owner.so
LoadModule authz_groupfile_module modules/mod_authz_groupfile.so
LoadModule authz_dbm_module modules/mod_authz_dbm.so
LoadModule authz_default_module modules/mod_authz_default.so
LoadModule ldap_module modules/mod_ldap.so
LoadModule authnz_ldap_module modules/mod_authnz_ldap.so
LoadModule include_module modules/mod_include.so
LoadModule log_config_module modules/mod_log_config.so
LoadModule logio_module modules/mod_logio.so
LoadModule env_module modules/mod_env.so
LoadModule ext_filter_module modules/mod_ext_filter.so
LoadModule mime_magic_module modules/mod_mime_magic.so
LoadModule expires_module modules/mod_expires.so
LoadModule deflate_module modules/mod_deflate.so
LoadModule headers_module modules/mod_headers.so
LoadModule usertrack_module modules/mod_usertrack.so
LoadModule setenvif_module modules/mod_setenvif.so
LoadModule mime_module modules/mod_mime.so
LoadModule dav_module modules/mod_dav.so
LoadModule status_module modules/mod_status.so
LoadModule autoindex_module modules/mod_autoindex.so
LoadModule info_module modules/mod_info.so
LoadModule dav_fs_module modules/mod_dav_fs.so
LoadModule vhost_alias_module modules/mod_vhost_alias.so
LoadModule negotiation_module modules/mod_negotiation.so
LoadModule dir_module modules/mod_dir.so
LoadModule actions_module modules/mod_actions.so
LoadModule speling_module modules/mod_speling.so
LoadModule userdir_module modules/mod_userdir.so
LoadModule alias_module modules/mod_alias.so
LoadModule rewrite_module modules/mod_rewrite.so
LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_balancer_module modules/mod_proxy_balancer.so
LoadModule proxy_ftp_module modules/mod_proxy_ftp.so
LoadModule proxy_http_module modules/mod_proxy_http.so
LoadModule proxy_connect_module modules/mod_proxy_connect.so
LoadModule cache_module modules/mod_cache.so
LoadModule suexec_module modules/mod_suexec.so
LoadModule disk_cache_module modules/mod_disk_cache.so
LoadModule file_cache_module modules/mod_file_cache.so
LoadModule mem_cache_module modules/mod_mem_cache.so
LoadModule cgi_module modules/mod_cgi.so

Save the file and do a:
service httpd start

For me, at least, this solved the problem and Apache started.

However, it seems that if you adjust your Apache settings in FC5 using the GUI tool, it will rebuild the httpd.conf file using the file:
/usr/share/system-config-httpd/httpd.conf.xsl

So you also have to go to this file, back it up, then edit it in the same way you did the httpd.conf file - replacing the LoadModule list.

A clever too for adjusting your Fedora firewall and disabling SELinux is system-config-securitylevel, which you can call from the command line with just its name (because it's in /usr/bin). The clever thing I just found out about it is that even connecting remotely from a Windows laptop to your Linux machine, via a PuTTY SSH session, it will pop-up a GUI window and allow you to reconfigure the settings point-and-click style.

Tomcat's still not working though!

Note:
The command /usr/sbin/getenforce displays the current SELinux level: Enforcing, Permissive or Disabled.

I'd forgotten how much faffing around is involved with Linux. I'm using a little 15" flat screen monitor and I changed the resolution from 800x600 to something higher, at which point the screen refused to display and I had to trawl the internet (via Windows on another machine) to find the solution, which is:

use the key combo:
Ctrl + Alt + [plus or minus key on the number pad] to cycle through screen resolutions.

Meanwhile, Tomcat is still proving troublesome to get up & running.

All this just so's I can install the trial version of Alfresco!

To reverse the sort, use the -r flag.

To restrict the output to a single column, use the -1 flag (that's a number one).

So, all together, to reverse sort the listing by date and format the list in one column, use the command:

ls -tr1

groupadd <groupname>

To create a user, create their home directory and add them to a group:

useradd -m -d <path/to/home/username> -g <groupname> <username>

To add an existing user to a group:

usermod -g <groupname> <username>

To find files in or below the current directory that contain the text string "if I only had a brain" enter the command:

find . -type f -print | xargs grep 'if I only had a brain' | more

Thanks to:
www.geocities.com/samarstan/linux/penguin/linuxuser.html
for reminding me how it was done on this occasion.

Answer:
Use the command:
ypcat hosts | grep "<IP address>    "

Where that space before the closing quote is a tab that you enter by pressing the TAB key.

Note: If you're in the bash shell you will need to press Ctrl+v before pressing TAB. Ctrl+v means "treat what I type next literally". (You're most likely to use it in vi when you want to enter or search for a control character. For example, if you want to delete all Ctrl+M characters you can enter :%s/^M$//g by pressing Ctrl+v Ctrl+M to give you the ^M character.)

For example, if you enter:

ypcat hosts | grep "192.100.123.456    "

The output will be something like:

192.100.123.456 hermes.yourorg.com hermes
192.100.123.456 hermes.yourorg.com hermes

In which case the host name is hermes.

See also:
Find an IP address given a host name

The first step is to use a long listing ls -l rather than just ls.

This lists the directory contents one per line, giving lots of information about each file and directory. The listing comprises 9 columns. If the first column start with a 'd' the item is a directory. If it starts with a '-', it's a file. The last column of the listing contains the file/directory names.

So what I want to do is:
1) Do a long listing.
2) Filter out the directories, based on the first letter of each line.
3) Remove everything except the last column, so that I have a simple list of files.

This is easily done using grep to filter out the listing and awk to print just column number 9. The following command uses pipes to pass the output from ls to grep and then on to awk:

ls -l | grep '^-' | awk '{print $9}'

If I'd wanted a list of directories, I could have changed the '-' to 'd':

ls -l | grep '^d' | awk '{print $9}'

uname -a

This returns something like:

SunOS sandbox 5.8 Generic_108528-13 sun4u sparc SUNW,Sun-Fire-280R

SunOS 5.6 is Solaris 2.6
SunOS 5.7 is Solaris 7
SunOS 5.8 is Solaris 8

An easy way to allow version details to be displayed is to use the UNIX what command.

Users then use the command what yourprogram to see the version details.

To implement this, add a line in your program containing the text string @(#) followed by whatever version details you want to give, followed by a double-quote mark or a line break.

For example, create a text file called what.txt containing the following:

Version numbers

To use the UNIX 'what' command
to return version information,
add a text string begining with an @ symbol
followed by (#) and everything following this,
until the line ending or a double quote
is returned to standard output by the
'who' command.

For example:
@(#)Version 1.0 - 'what' command explanation

Now if you run the command
what
you will see:
Version 1.0 - 'what' command explanation

See
man what
for more information.

Now run the command what what.txt and what prints the message:

Version 1.0 - 'what' command explanation

To change your default vi settings, edit ~/.exrc. For example, add:

set showmode
set number

This displays the current mode (e.g. "INSERT MODE") and displays line numbers.

To temporarily remove the line numbers (e.g. so that you can copy lines without copying the numbers) use the following command in vi:

:set nonu

The only fly in the ointment is a little tiny gnat that you can soon get rid of. The first time you try to use yum you will probably get a message like:

You have enabled checking of packages via GPG keys. This is a good thing.
However, you do not have any GPG public keys installed. You need to download
the keys for packages you wish to install and install them.
You can do that by running the command:
    rpm --import public.gpg.key
For more information contact your distribution or package provider.

This means you need to tell yum who it can trust. You do this by installing Fedora security keys:

rpm --import /usr/share/rhn/RPM-GPG-KEY*

Note
You have to do all this as root.

For more information, see:
www.hut.fi/~tkarvine/yum-package-manager.html

You can use yum to update your whole system, and it's recommended that you do this every now and again. However, be advised, the first time you do this it's going to take a long while. First yum produces a list of everything that needs to be updated. This takes a while, at the end of which you are asked to confirm that it's okay for yum to proceed. If you answer yes, yum will start downloading all of the necessary packages.

As I write, yum is still updating 383 packages on my Fedora machine, so I can't tell you how long it's likely to take, but I think it's been running for about an hour already!

To update your system, enter the command:

yum update

A: Run an RPM query to return the details of all the installed RPMs, and use grep to filter the results.

For example, I just wanted to check which DocBook RPMs, if any, were installed on my machine. The command:

rpm -qa|grep -i docbook

Yielded the reply:

docbook-slides-3.3.1-2
docbook-dtds-1.0-25
docbook-simple-1.0-2
docbook-style-xsl-1.65.1-2
docbook-utils-0.6.14-4
docbook-utils-pdf-0.6.14-4
docbook-style-dsssl-1.78-4

date

And compare the results with the output of the command:

rdate -p <server>

where server is one of the following:

table.bespoke {
border: 1px hidden #342DAC;
border-collapse: collapse;
background-color: #F3FEFF;
}
table.bespoke th {
border: 1px outset #342DAC;
background-color: #FFFFF0;
}
table.bespoke td {
border: 1px outset #342DAC;
padding: 2px;
}
table.bespoke .country {
text-align: center;
}

For example:

# date
Tue Feb 22 08:55:06 GMT 2005
# rdate -p ntp.demon.co.uk
rdate: [ntp.demon.co.uk]        Tue Feb 22 08:50:14 2005

In the above example, the local machine is about 5 minutes fast.

rdate -p <server>

prints the date from the remote server.

To set your Linux machine to that date, use:

rdate -s <server>

For example:

rdate -s ntp.demon.co.uk

You can use ntpd to check and set your time on a regular basis, but if keeping accurate time isn't critical for you, the occasional manual check and reset is all you need.

For more information, see: http://linuxreviews.org/howtos/ntp/

I'd never heard of either command (probably because they're not in my copy of UNIX Complete - probably because it's from 1999).

Using pkill allows me to replace the following, from a shell script that stops or starts a program called lmgrd:

kill `ps -ef | grep "lmgrd -c" | grep -v grep | awk '{print $2}'`

with this:

pkill lmgrd

Check out the man page for pgrep and pkill (or read it online at http://linux.about.com/library/cmd/blcmdl1_pgrep.htm)

C shell (csh)
To add your home directory (~) to your PATH, add the following to the .cshrc file in your home directory:
set path = ($path ~)

Bourne shell (bash)
To add your home directory (~) to your PATH, add the following to the .bashrc file in your home directory:
PATH="$PATH:~"; export PATH

Your changes take affect the next time you log in. To apply your changes now, run the following commands.

C shell (csh)
source .cshrc

Bourne shell (bash)
. .profile

For example, to check whether there's a user called alistair, run the following command:

cat /etc/passwd | grep "^alistair"

Note: This will also find users called "alistair1", "alistair2" etc. If you grep for just "alistair", you will find users like "thisalistair" and thatalistair".

Search the group file in the same way to check for existing groups. For example:

cat /etc/group | grep "^adminusers"

A case in point is how to find out how much space you have left on a Linux machine.

The answer, of course, is to use the df command. For example:

# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/hda3              73G  3.0G   66G   5% /
/dev/hda1             244M  8.7M  222M   4% /boot
none                  157M     0  157M   0% /dev/shm
/dev/hdb1             7.8G  183M  7.2G   3% /home

The -h flag here outputs the results in human-readable format - i.e. it appends M for megabytes and G for gigabytes, rather than printing everything in kilobytes.

To find out stuff like this you can, of course, search the Internet. But a more efficient way - at least for starters - is to search the man system using the apropos command.

For example, to search for man pages that mention "disk space":

# apropos 'disk space'

When I do this, the result is:

df        (1)  - report filesystem disk space usage

cvs log <filename> | grep author | awk '{print $5}' | sort -u

Replace <filename> with a real value.

Thanks to Sandy Dunlop for this tip.

Say you've got a file called johnbrown.txt containing the following text:

This file is the property of John Brown.
John Brown will be very annoyed if anyone alters it.
Signed: John Brown.

Run the following command:

sed -e s/John Brown/Jill Green/g johnbrown.txt > jillgreen.txt

You now have a new file containing the following:

This file is the property of Jill Green.
Jill Green will be very annoyed if anyone alters it.
Signed: Jill Green.

Not much use for a three-line file, but very handy for a 3000-line file.

Find out more about sed at:
http://pegasus.rutgers.edu/~elflord/unix/sed.html

If you want to do anything more complex than this (i.e. match whole words only, or match across multiple lines) then you can do it in sed, but it's painful. You're much better switching over to Windows and using Replace from Eluent Tools.

www.interopsystems.com/tools/warehouse.htm

For example:

OpenSSH
bash
vim
Apache

To install these, you need to install the package installer.
You do this by going to:

ftp://ftp.interopsystems.com/pkgs/3.5/

and downloading a shell script called pkg-1.6-bin35.sh, or similar (there might be a newer release by the time you read this). For example, save it to your SFU root directory (usually C:\SFU).

After downloading, run the script from an SFU shell prompt.

This adds the programs pkg_add, pkg_info, pkg_delete, pkg_create and pkg_sign to /usr/local/bin.

Download the package you want to install (e.g. OpenSSH at ftp://ftp.interopsystems.com/pkgs/3.5/openssh-current-bin.tgz) unzip it, then run the package installer on it, e.g:

pkg_add openssh-current-bin.tar

The above example adds SSH, so that you can login to the machine using SSH (e.g. using PuTTY).

Solution:
Use tr to transform the path string. For example, the path to the directory you are backing up (/dev/fs/D/mydir) is stored in the variable $DIRECTORY. Use the following commands to create a variable called $NAME containing BACKUP_.dev.fs.D.mydir.

NAME = `echo $DIRECTORY | tr '/' '.'`
NAME = BACKUP_`echo $NAME | tr '\' '.'`

Note: don't mix up the backticks and the single quotes.

For a full description, see:

www.itauthor.com/unix_linux_shell/shell-backup-script.html

For example, if you want to list only the files beginning with a full stop ("."), you can use the command:

ls -a | grep '^\.'

Note: if you're going to be using \ or * you need to enclose the expression that you pass to grep in single quotes.

I frequently want to list just the directories within the current directory. This is especially useful in a directory with lots of files. To do this I use the command:

ls -l | grep ^d

Which produces something like:

drwxr-sr-x   2 me    mygroup   512 Mar  1  2002 News
drwx--S---   2 me    mygroup   512 Dec  8 12:42 Trash
drwxr-sr-x   3 me    mygroup   512 Jan  9 15:59 cvs
drwxrwsrwx   7 me    mygroup   512 Apr 14 00:28 documents-archive
drwx------   2 me    mygroup   512 Aug  4  2003 downloaded-files
drwx------   2 me    mygroup   512 Sep 18  2002 mail
drwxr-sr-x   3 me    mygroup   512 Feb 11 23:03 perlprogs
drwxrwsrwx   2 me    mygroup   512 Apr 13 23:44 temp
drwx------   2 me    mygroup   512 Aug 28  2003 upload-from-here

If you're only interested in the directory names use:

ls -l | grep ^d | awk '{print $9}'

Which prints only column 9, giving you:

News
Trash
cvs
documents-archive
downloaded-files
mail
perlprogs
temp
upload-from-here

For more information on awk, see:

http://www.linuxfocus.org/English/September1999/article103.html

http://tille.soti.org/training/awk.php

Answer:
The easiest way is to use the command:
ping hostname

This will normally return something like:
PING humphrey (192.168.1.100) 56(84) bytes of data.
64 bytes from humphrey(192.168.1.100): icmp_seq=0 ttl=64 time=0.088 ms
64 bytes from humphrey(192.168.1.100): icmp_seq=1 ttl=64 time=0.081 ms
64 bytes from humphrey(192.168.1.100): icmp_seq=2 ttl=64 time=0.086 ms
64 bytes from humphrey(192.168.1.100): icmp_seq=3 ttl=64 time=0.084 ms

and you press Ctrl+C to stop the process.

However, sometimes ping will be set up so that it isn't so informative. It may just reply:
humphrey is alive

in which case you have a couple of alternatives.

If you want to find the IP address of the current UNIX machine you can use the command:
cat /etc/hosts | grep `hostname` | awk '{print $1}'

Note that the first quote marks are backticks (you can replace `hostname` with the host name of the current machine if you prefer, but this makes the command less portable), and the second set of quote marks are normal, straight, single quotes.

If this doesn't work it's probably because you aren't allowed to see the contents of /etc/hosts, but most system administrators trust their firewall enough to leave this file readable by domain users.

If you want to find out the IP address of another machine on the network, try:
ypcat hosts | grep hostname

See also:
Find a host name given an IP address

Redirection of standard output is easy:
> in most cases
< to go the other way
>> or << to append.

Redirecting standard error is the one I tend to forget.

In the C shell you can use the following to redirect standard error:

(command) >& file

For example:

(tar cvf tarfile.tar myprogramdirectory) >& log.txt

This tars up a directory and sends the verbose output to the log.txt file,
rather than the screen, so that you can peruse it later.

You can redirect standard output and standard error independently like so:

(command > outputfile) >& errorfile

For example:

(ls mydirectory > directorylisting.txt) >& ls_error.txt

This sends a directory listing to a text file.
If there's an error (e.g. there's no such directory)
the error message gets put in the ls_error.txt file.

In bash (and most other shells), you use 2> to redirect standard error.
So the bash version of the previous example is:

(ls mydirectory > directorylisting.txt) 2> ls_error.txt

First up, a recap on tarring and zipping.
Tarring pulls a directory full of files and subdirectories together into a single file. Zipping a file compresses it.

> To tar a directory use the command:

tar cvf destinationfile.tar directory

This creates a file called destinationfile.tar containing the entire contents of the directory called directory (including any subdirectories). The c flag means create (rather than append to an existing file). The v flag means use verbose mode (i.e. print a notification of each file that is tarred). The f flag means you're going to specify the name of the tar file rather than using the value of the TAPE environment variable or the default value defined in /etc/default/tar.

The verbose details get printed to standard error, which is the screen by default. You can redirect standard error to a file if you want to capture the output. This is a good idea if you are tarring a lot of files, otherwise the details of any problems appear briefly on the screen before being replaced by more information. If you capture the verbose details you can check what happened when the process completes. To capture the verbose details for the previous example:

In the C shell:

(tar cvf destinationfile.tar directory) >& log.txt

In bash:

(tar cvf destinationfile.tar directory) 2> log.txt

> Once you've got your tar file, nine times out of ten you're going to want to zip it.

To zip the tar file, use gzip:

gzip destinationfile.tar

This replaces destinationfile.tar with a compressed file called destinationfile.tar.gz. If you want to keep the original tar file, take a copy of it before zipping it.

> To unzip a file zipped with gzip, use gunzip:

gunzip destinationfile.tar.gz

As you'd expect, this replaces destinationfile.tar.gz with a decompressed file called destinationfile.tar.

> To untar your tar file:

tar xvf destinationfile.tar

This unpacks the tar file, recreating the original tarred directory as a subdirectory of the current directory. If a directory of the same name already exists the files from the tar file are added to it, overwriting any files of the same name. Existing files with different names are not removed. The tar file is not deleted.

> If you want to see what's in a tar file, without going to the lengths of untarring it, use the command:

tar tvf tarfile.tar

The t flag lists the table of contents for the file. If you want to check whether the tar file contains a file called myfile.fm, you can use the command:

tar tf tarfile.tar *myfile.fm

If you want to check for files called alsfile.txt, alistairsfile.fm, bobsfile.doc, etc. you could use the command:

tar tvf tmp.tar | grep .*sfile\....

The \. is the dot character. The final three dots is the regexp way of saying any three characters.

Using this method, you can untar selected files. For example, to untar just files whose names end .fm use the command:

tar xvf tarfile.tar `tar tf tarfile.tar | grep \.fm$`

In this command the dollar sign is the regexp way of denoting the end of a line.
This command would unpack all the .fm files, recreating the directory structure in which they originally lived.

If you are untarring a single file and you don't want to recreate all the directories that originally housed it, but you just want the file to be unpacked into the current directory, you can use the following syntax:

tar xvfO tarfile.tar *myfile.txt > myfile.txt

The O flag (that's a capital "oh") isn't documented in the man page, but I just tried it and it had the desired effect. It sends the output of the process to standard output, which allows you to redirect it to a file.

However, beware! If you use a command such as:

tar xvfO tarfile.tar `tar tf tarfile.tar | grep .*file\.txt$` > myfile.txt

you are asking for trouble, because more than one file may be matched by grep and unpacked by tar, and the contents of all of the unpacked files will end up in the specified output file (myfile.txt in this case).

See www.informationweek.com/story/showArticle.jhtml?articleID=17300643 for the full story.

The company I work for uses SFU to provide its server-side software on Windows servers. The code was originally written to run on UNIX (most of it tailored for Solaris) but SFU provides and easyish way to port to Windows.

Personally I like SFU. It's a big improvement on its predecessor (Interix), and it works pretty well. It allows you to have something very like UNIX running on your Windows machine, without having to dual boot or run VMware, and in my experience it's much easier to install and maintain than cygwin.

So I'm very pleased that 3.5 will be free. However, my main SFU gripe is that you can't install it on XP Home, which is what I have on my main home PC. It will only install on Professional – either Windows 2000 or XP. This means when I'm working from home I have to use my Win2k laptop as the server and my main desktop as a client. My Dell Latitude takes ages to boot up, so this setup can be a pain. Will 3.5 run on XP Home? Guffaw, guffaw!

The site also includes a paragraph headed What happens on July 8, 2038?, which describes the UNIX date of death, when 32-bit processors run out of numbers for date stamps.

Another site I came across that might be useful if you're looking for a quick and basic introduction to XML is Learn XML in 11.5 minutes.

I spent some time over the weekend starting to design the home page for this website. Lots more to do, so I haven't uploaded anything yet, but it should be ready before too much longer.

5.3. Search & Replace
To search for a regular expression (see section Regular Expressions) press slash, type the pattern and then start search with the enter key. vi jumps to the first occurrence of the specified pattern. To go to the next occurrence, press 'n'.

Replacing is done using the ':s' command. Type ':s/pattern/replacement/g' to replace all occurrences of pattern with replacement in the current line.
Most of the time you want to work with the whole file, though. That is done using the ':%s' command. Use ':%s/pattern/replacement/g' and pattern is changed to replacement in the whole file. If you aren't sure whether you really want to replace all occurrences, you can append the character `c' at the end of the line. This stops at every occurrence of the pattern and asks if you really want to replace.

Source: http://www.ibiblio.org/gferg/ldp/practical_linux_guide/x360.html