HOW TO USE THE LINUX TERMINAL

by Donald Daniel, 2010, revised May 2019

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If the lines of text are too long you can fix the problem with these instructions.

GETTING STARTED

This article teaches linux for beginners. This is based on Debian linux, but will mostly apply to any version of linux. It assumes that the linux installation included "gnome desktop" and "standard system". If you have not yet added linux to your windows computer instructions are provided here.

This introduction to linux is designed to get you started quickly. If you need a much more lengthy and detailed article see http://tldp.org/LDP/intro-linux/html/.

These instructions emphasize features of linux that are different from Windows. You must first login then you will see the gnome desktop screen. Make sure that you log in as an ordinary user, not as superuser. In the top left corner of the gnome desktop screen you will see "activities". If you click on that, below it will be some icons to select some of the more popular software. If you click on these items they will work in a way that will be familiar to windows users, though not identical to windows. In the upper right corner of the screen will be an array of symbols. If you click on it, a black window will open below it. At the bottom of the black window will be three symbols. If you click the symbol on the right, a new window will appear that will give you the choice to "power off" that you will use to shut down the computer.

Click on "activities". One of the icons, a three by three array of dots, will let you see "applications" when you click on it. To the right of the array of application icons will be a vertical column of four small circle icons. Click on each circle icon to see a different set of application icons. The terminal icon will be revealed after you click on the utilities icon. The terminal icon is a gray rectangle. Right click on the terminal icon and click on "add to favorites" to make the icon appear on the desktop so it is easier to get to. The real power of linux will be accessed from a terminal window, and that will be the focus of this course. You can open more than one terminal window at a time. To do this, in the first terminal issue the command "gnome-terminal" and another terminal will open. You could also right click in the terminal window to open another terminal window.

Click the mouse anywhere in a terminal window to activate the terminal. Anytime you are instructed to type a command, hit the "enter" key afterward, since no command takes effect in linux until you hit "enter". Then enter "pwd", which means "print working directory". Directory in linux means the same as folder in windows. You will see something like "/home/yourname" where "yourname" is whatever user name you picked when you installed linux. Next, enter "cd /", then enter "ls". "ls means "list". You will next see the following list of directories and files: bin boot cdrom dev etc home initrd.img lib lost+found media mnt opt proc root sbin selinux srv sys tmp usr var vmlinuz.

You are now at the root directory of the file system, "/". This is like being in the machinery part of a ship, where the engine, electrical, air conditioning, water and sewage machinery is. Most of the stuff you see is the machinery of the operating system. The directory "home" is like the passenger section of a ship. Now enter "cd", then enter "pwd" and you will see that you are back in your home directory. The command "cd xyz" will move you to a directory named xyz, if it exists, that is contained in the directory where you are currently located. By contrast the command "cd /xyz" will move you to a directory that is located in the "/" directory.

In your home directory enter "mkdir wkspc". "mkdir" means "make directory". Then enter "ls". You will see the new directory "wkspc" that you have just created with the command "mkdir". Now "cd wkspc". Now you are in the directory "wkspc". Now enter "mkdir back ltr photo scratch". Now enter "ls" and you will see the directories you have created to hold your backup files which will be saved to a USB stick to save valuable personal data in case of a hard drive failure, letters or emails that you have written, photographs you have loaded onto your computer, and a scratch directory where you can do messy work that you only want to retain temporarily.

Enter "cd scratch" to get into your scratch directory. Next you should learn the vi editor, and in your scratch directory create some little unimportant file of nonsense called "xyz" that you can experiment with.

Now enter "cp xyz abc". "cp" means "copy". Then "ls". You will see that you now have two files, "xyz" and "abc". Look at them with the vi editor and see that they are the same. Now enter "rm abc", then "ls" and you will see that you have removed "abc".

There is an easy way to refer to certain directories. Your home directory is "~". The directory where you are at any given time is ".". The parent directory of where you are is "..". If you are in your scratch directory, enter "pwd" then "ls", then enter "cp xyz ~". You have now made a copy of xyz in your home directory. Enter "cd .." then "pwd" and "ls". You are now in your wkspc directory. Again "cd ..", "pwd" and "ls". You are now in your home directory and can see the copy of the file xyz that you just made. Now "cd wkspc/scratch", "pwd" and "ls", and you see that you are back in your scratch directory. Now in your scratch directory and enter "rm ~/xyz" and you have removed the copy of xyz in your home directory.

Now in your scratch directory enter "cp xyz t1", "cp xyz t2", "cp xyz t3", then "ls". You now have xyz, t1, t2, and t3 in your scratch directory. Now we use the wildcard character *. Enter "rm t*" then "ls", and you will see only xyz remains, the others have been removed. By saying "t*" we referred to everything starting with "t". If we had said simply "*" we would have removed everything. "rm" just removes files. "rm -rf" removes both files and directories. You are doing this as an ordinary user, not a superuser, or root, as superuser is also called. As an ordinary user you cannot remove any of the stuff you saw in the directory "/". But as superuser you could. This is VERY DANGEROUS!!! Be very careful what you do as superuser. If at "/" as superuser you did "rm -rf *" you would remove your whole linux system!

If you want to move a file from one place to another, you could "cp" to create the new version then "rm" to delete the old version, but it is simpler to just "mv" which means "move". "mv" can also be used to rename a file without moving it. "mv xyz uvw" changes the name from "xyz" to "uvw". To copy a whole directory and not just a file, use "cp -r" and the name of the directory. "ls" will list directories and files, but you may not know which is a directory and which is a file. There are also hidden files with names having "." as the first character. To list all directories and files, including the hidden ones, use "ls -aF". In your home directory you will see some hidden files. Directories names will end in "/" to distinguish them from files. To see the size of files and other information about the files do "ls -l".

To see how much of your filesystem is used enter "df". The entry "/dev/hda2" or similar which is mounted on "/" is the important one. To see how much space is used by each directory enter "du -bhs *". Similarly, to find the size of file xyz enter "du -bhs xyz".

USING THE BROWSER

The way the Firefox browser is initially set up you cannot view html documents that are on your own computer, not on the internet. To fix this, click on the icon with three horizontal bars, "customize", right click on "open files", click on "add to toolbar". Now you have an icon that will let you see local files.

The browser operation is not as obvious as it should be. The default way to print is with ridiculously small margins. To set the margins, click on the icon with three horizontal bars, then "print", "page setup". In "manage custom sizes", change the margins to one inch, "close", "apply".

If you would like to add the Chrome browser, the best way to do that is by installing it with the debian synaptic program, described later.

BECOMING SUPERUSER

As previously noted, becoming superuser gives you a dangerous amount of power. Only become superuser to carefully do a task that requires you to be superuser, and cease to be superuser as soon as the task is completed. To become superuser, in a terminal window enter "su", then you will be prompted for your superuser password. When you are not superuser, the prompt character at the left of the terminal window will be "$". When you become superuser the prompt character will change to "#". When you are ready to cease to be superuser, in the terminal window enter "exit". As superuser you can shut the system down with "shutdown -h now". You can move executable scripts or user created software to /usr/local/bin. Various other special tasks may require you to be superuser.

FINDING INSTRUCTIONS

There are several sources of information contained in your linux system, and if these fail, you can google your question and probably find and answer.

To find out how to move things we would enter "apropos move". A list of commands related to moving will be shown. If the list ran off the screen we could contain it with "apropos move | more". The "more" command limits the size of lists to one screen at a time, with the space bar being used to see the next screen full of a long list. If we want to find out more about a command in the list, such as "mv", we would enter "man mv". "man" means "manual" or "handbook". Most commands have a "man page". An exception is "cd". This is because cd is not really a stand alone command, but is part of bash, so "man bash" will contain an explanation of cd. Bash is a program that starts running automatically when you open a terminal window. Its purpose is to create a user friendly environment.

There other places containing instructions, most notably in /usr/share/doc. If you do "ls" the list will scroll off the screen, so to "ls | more", then hit the space bar to see each screen of the list. These are all directories. Most of the files in these directories end in ".gz". The vi editor will not read these. Instead, to read "file.gz" enter "zless file.gz". This will unzip the file into the vi editor.

ADDING SOFTWARE

If you cannot find software on your computer to do what you want, you can probably add the software free of charge. If you add free software available from debian, you will be sure that it is compatible with your operating system. If you are not sure of the name of a software package that will do what you want, you can use descriptive terms to search for it in the synaptic package manager program. Enter "su" and your superuser password, then enter "synaptic", and then click on "search" and enter the name of the package you want. When you click on search a "find" window will pop up. In the find window is a "look in" bar with different options. Sometimes one option will find what you want and another option will not. You will see an alphabetical list containing the package you want. Scroll down the list until you see the package you want. You can scroll by dragging the cursor or by using the down arrow key on your keyboard. Click on it to see a description. If it is really what you want click on the tiny square to the left of the package name to select it for installation. The package you selected may depend on additional packages, which will automatically be selected also. When you have found and selected all the packages you want, click on "apply". When the process is all finished, exit the synaptic program and be sure to enter "exit" to quit being superuser and go back to being an ordinary user.

To get the google chrome browser in synaptic select "chrome-gnome-shell". This will install it in a way that is guaranteed to be fully compatible with debian linux. Your interests may be totally different than mine. Other packages I download are: g++, make, libtool, libgc-dev, dcraw, mmv, xfig, xfig-doc, tidy, gv, vorbis-tools, cdrskin, geomview, texlive-latex-base, remind, sox, xorriso, wodim, cdparanoia, unhtml and pstoedit. These together with the linux operating system only occupy only a small amount of the hard drive capacity.

If you are not sure whether you have a certain piece of software on your computer, see if it is marked as installed in the synaptic program, or use the "whereis" command. Thus "whereis vi" will yield "vi: /usr/bin/vi /usr/share/man/man1/vi.1.gz" which shows where the various parts of vi are stored. But "whereis dog" will simply show "dog:" meaning that you have no such program.

I have an HP printer. I had to run a program included in linux called "hp-config". That downloaded and installed the software driver for the printer. After that the printer worked. I do not know how to do the same for other printers, so search the internet if you need to.

If you use your computer regularly, from time to time, linux will automatically add updates to your existing software. If you have a laptop that you only use on trips, it will not be updated when you need it for a trip. If you would like to force an update to make sure you are up to date, here is how. Open a terminal. Become superuser. Enter "apt-get update". When the "#" re-appears at the beginning of the line, your machine now knows what packages need to be updated. Next, enter "apt-get upgrade", and the packages will be brought up to date. Remember to "exit" when you are through.

If you want to discover the wide range of programs available to download with synaptic go to http://packages.debian.org /stable and look for what you want.

To see a list of the software packages that are already installed, enter "dpkg --get-selections > temp" then use the vi editor to look at the list in the file temp. This procedure will only list debian packages. Software obtained from other sources will not be included.

EXECUTING PROGRAMS

If the program is located in one of the "bin" directories just typing the name of the program in an active terminal will execute it no matter what directory you are in. The main bin directory is "/bin". You can see it listed if you type "ls /". When you use the synaptic package manager to install programs they will be put in that bin directory or a bin directory at a lower level. You should never tamper with these directories yourself, let synaptic do it. If you want to install a program by hand yourself, put it in /usr/local/bin, which is for use by all users. You must be superuser to do this.

If the program "xyz" is not in one of the bin directories, but is in the directory where you are, typing "xyz" will do nothing. Instead, type "./xyz" which will execute it. Notice the period before the slash. If you are in a directory below your home directory, but wish to execute a program or script that is located in your home directory, "~/xyz" will do that.

If you create a bash script with the vi editor, you must use the chmod command to make it executable. In your scratch directory enter "vi scr" to create a text file named scr. In scr create the following text which is a bash script:

# this is a demo script
echo dog
echo $1
echo cat 

The "$1" means the first thing after the name of the script that is on the same line as the name of the script when you execute the script. After creating this script enter "chmod +x scr". That makes the script executable. Then to test it enter "./scr elephant". The following results:

./scr elephant
dog
elephant
cat

While the above example of a script is of no practical use, later in the "tools" section of this web page you will see other examples of scripts that are of practical use. Hopefully after seeing several scripts you will have the confidence to try making a script yourself if you feel you need one.

There are books on bash, or you can do "man bash" to find out more. I only do simple stuff with it, but some people do very complicated things with it. It is much more difficult to learn to program in bash than in my favorite language, oberon-2. The above example could have been programmed in oberon-2, but it would have been more time consuming to do. But it is very straightforward to write complicated programs in oberon-2. It is a nightmare to write complicated programs in bash. Bash is best for simple things.

If you start a program running, and it keeps running longer than you want, you can usually stop it by holding down the "ctrl" key and at the same time hitting the "c" key. This is usually described as "control-c" or "ctrl-c".

USING USB PORTS

About once a month you should backup your personal files, saving them on two USB sticks, so that if your hard drive fails you will not lose your work. You do not need to be superuser to do this. First, copy all the files you must save to your backup directory, wkspc/back. Then enter "mount". Notice the last line of the listing. Insert a USB stick into a USB port on your computer. A large rectangular window may pop up, get rid of it, we will not use it. Enter "mount" again. Notice a new line added to the end of the listing, something like "/dev/sdb1 on /media/(yourname/2365-21A3 type vfat ...". Minor details may be different on your computer. In fact the number may be different on your computer each time you insert a USB stick. This tells us the the USB stick is /media/(yourname)/2365-21A3. Now "cd /media/(yourname)/23*". Here the "*" is a wildcard so you do not have to type the whole thing. Then "ls" to see what is on the USB stick. Do "rm -rf *" to erase the USB stick. Then "cp -r ~/wkspc/back .", where the final "." means put the copy in the directory where you presently are, the USB stick. If there is a lot of stuff, this may take a while before the cursor re-appears. Do not be deceived, the copy is not finished at this point. Enter "sync" and wait until the cursor re-appears. For small files, you might get a complete copy without using sync. But for large files you probably will not get a complete copy unless you use sync. Now the copy is finished. To make sure the copy is a good one, enter "diff -r back ~/wkspc/back". If no errors appear the copy is a good one. First "cd" to your home directory, then you can remove the USB stick. It is best to make backup copies on two USB sticks just in case one of them should fail for some reason, and keep them stored in separate places.

You will sometimes want to re-format a USB stick. One time I wrote a file on a USB stick and took it to be read by another computer. The person used commercial application software to read the file off the stick. But the application software corrupted the stick so I could no longer write to it. So it needed to be re-formatted. Here is how. Do not put the stick in the computer yet. Open a terminal window. Enter "mount". Write down the first few words of the last line. Put the USB stick in the computer. Enter "mount" again. Notice that a new line has been added after the last line. It might be something like "/dev/sdb1 on /media/yourname/23...". If you enter "cd /media/yourname/23*" you will be in the USB stick. "ls" will show what is on the stick. But you must not be on the stick to re-format it, so "cd" to get back to your home directory. Enter "su" and the superuser password so that the first character on the line changes from "$" to "#". Enter "umount /dev/sdb1" so that the stick is no longer mounted but it is still in the computer. If the stick is 4GB or less, enter "mkfs.vfat /dev/sdb1" to re-format the stick with a new vfat file system. If the stick is greater than 4GB then enter "mkfs.exfat /dev/sdb1". Enter "exit" so you are no longer superuser. Now "mount" will not show the stick. Remove the stick and re-insert it into the computer. Now "mount" will show the stick. "cd" to the stick at "/media/..." and "ls" to see that it is now a blank re-formatted stick. To see how much space is on the stick enter the command "df -h ." . The period "." after "-h" means the current file system, not the current directory as it would with other commands.

You may wish you could plug an SD memory device from a digital camera into your computer, but your computer does not have an SD port. No problem. You can purchase an inexpensive adapter a little larger than the average USB stick. The adapter has large and small SD ports in it, and a USB plug that you can plug into the USB port on your computer.

Your computer may not have an internal optical drive for reading and writing to CD's and DVD's. You can purchase an inexpensive external optical drive that you can plug into your USB port. Linux will support this so it will work exactly like an internal optical drive.

You may want to make a bootable USB stick so you can install linux on a friend's windows computer. You would want to put the debian "netinst.iso" file on the stick to boot into the debian install program. But this must be done in a special way or it will not be bootable. If you plug the USB stick into your computer and enter the command "mount", the last line of the display will be something like this:

/dev/sdb1 on /media/(yourname)/(stick ID)

If you tried to copy netinst.iso to /media... it would not be bootable. If you tried to copy netinst.iso to /dev/sdb1 it would not be bootable. But if you leave off the "1" and copy netinst.iso to /dev/sdb it will be bootable. But remember you may have to change settings in the BIOS of your friend's computer, and repeatedly tap a special key during boot up in order to boot into the debian install program.

STANDARD OUTPUT

Some programs put their output to "standard output", which is the screen. Thus the command "ls" will list the files in the current directory on the screen. But suppose you want the list in a file. "ls > temp" will put the list in the file "temp". The ">" redirects standard output to a file. If you wanted to print the file you could enter "lpr temp". But you could use a pipe, "|", instead. Thus "ls | lpr" will pipe the output of the "ls" command to the "lpr" command and the list will be printed.

The command lpr probably originally stood for "line printer". The original computer printers were either mechanical line printers or mechanical accounting machines that could also print. Originally they took data from punched cards, later directly from the computer from commands such as "lpr". In 1963 I used an IBM 407 accounting machine that read cards. It was about 51 inches high, 73 inches wide, and 31 inches deep from front to back. It weighed 2620 pounds. It was mounted on springs and rocked back and forth as it printed a line of text at a time on a long stream of fanfold paper.

LINUX TOOLS

You could spend a lifetime mastering all the tools in linux. Here is a sample to familiarize yourself with the sorts of tools that are available.

There are many ways in linux to make hard jobs easy. All of the tools mentioned here are free software. Finally, you should get yourself a bound book of lined notebook paper and title it "howto". Every time you figure out how to do something in linux, enter it in your "howto" book. This will save you the frustration of having to figure out the same thing twice.

Suppose you want to find all occurrences of the word "glue" in every file in every directory at and below where you are. "grep -r glue *" will do this. "grep -c glue *" will count the number of times the word "glue" appears in every file in the directory where you are. If you want a file named "temp" that contains all the lines in "myfile" containing the phrase "I want this line" then "grep 'I want this line' myfile > temp" will do it. Then the command "wc -l temp" will tell the number of lines in the file temp. Grep is a powerful tool for analyzing the use of your website that is recorded in a logfile of hits. You can find how often one part of your website is found by linking from another part of your website. Or, consider the command grep -E -c -v windows\|mac\|android temp. This will find the number of lines in the file temp that do NOT contain the words windows or mac or android. If you want to find a file name, and not the contents of the file, then "find -name xyz" will find file named xyz.

Suppose you have downloaded a suspicious file and you want to find out what kind of file it is. The command "file *" will list every file in the directory where you are and tell what kind of file it is.

You will probably want to install the "zip" program so you can use zip files. If you want to create fancy pdf documents you will want "texlive-latex-base". If you want to convert an html document to pdf format, "htmldoc" works well, but skips graphics in the html document.

For hearing some types of audio files you will need the "vorbis-tools" package. For some video work you will need "cdrskin".

For drawing things, you could use the openoffice draw program which comes with your debian installation, which I have never tried. I use the older program "xfig".

To see graphics files or pdf files click on "applications" "system tools", "file browser", then click to find the directory where the file is. But if you are in a terminal window where the file is, it would be quicker to use a command to display what you want to see. If the imagemagick package is installed, "display xyz" will display the graphics file xyz for most formats. If "gv" is installed, "gv xyz" will display pdf files and postscript files.

Suppose you have a list of old movies in the form title, year, comments in a file named "list" like this:

show people, 1928, m
the battle of the sexes, 1928, dw griffith
the patsy, 1928, documentary following movie

You can sort this list by year, and within each year alphabetically with this bash script:

sort -t , -b -k 2,2 -k 1,1 list > temp
mv temp list

When you first use the vi editor to create this script in a file arbitrarily called "srt", "ls -l srt" will show that it is not executable. Make it executable with the command "chmod +x srt". Now "ls -l srt" will produce different results showing that it is executable. Then to sort your list enter "./srt". Each field title, year, comment is separated by a comma. In the script we have chosen the comma as a separator. So if a title had a comma in the title, the comma would have to be left out for the sort to work properly.

There are many linux commands that change a file from one format to another format. This includes text files, graphics files, audio files, etc. Suppose you want to change a large number of files in one format with one suffix to another format with another suffix. File suffixes matter to the windows operating system, but they do not matter to the linux operating system. Suffixes do matter to some programs in linux. Take a trivial example of files like "t1.txt" that are lower case with "txt" suffix. You want to make them upper case with "caps" suffix. The command "tr 'a-z' 'A-Z' < t1.txt > t1.caps" would do this. But it would be a lot of work to do this for t2.txt, t3.txt, ...t100.txt. The following script is a program written in bash that will do this all at once:

#  make caps files from txt files
namechange ()
{
oldname=$1
newname=${oldname%.txt}.caps
echo "$newname"
tr 'a-z' 'A-Z' < $oldname > $newname
}
for filename in "$@" ; do
namechange "$filename"
done

If we arbitrarily choose to call the script "proc", then "chmod +x proc" will make it executable. "./proc t1.txt" will perform the operation for t1.txt. But "./proc *.txt" will perform the operation for all of the files in the directory with "txt" suffix. For some other format changing command and other suffixes, you could change the suffixes in this script and change the command line. If your line is too long, end it with "\" and continue on the next line, but you must be careful that the "\" is the last character on the line, and there is no invisible space character " " following it. The line starting with "#" is just a comment, and has no effect.

The command "mv" for moving and renaming files comes with linux. But you might want to install the more powerful command "mmv". Suppose you have a list of files like "access_110606.log", "access_110613.log", etc. representing log files for the month of may. The command [mmv "*1106*.log" "may-#2"] would change the names to the simpler form "may-06", "may-13", etc. Here the brackets [] are not part of the command, but are used because the double quotes " are part of the command.

My favorite linux tool is oo2c, which I use to program the computer when I want to accomplish something for which there is no built in function. It is not available from debian, and must be installed without the help of synaptic. It is very easy to install following the instructions in the above link. It automatically installs in /usr/local/bin.

If you want to save an example of a detailed procedure so that you can email it to someone or remember how you did it, the "script" command is useful. Before you start your procedure type "script". Then after completing your procedure hold down the "ctrl" key and type the letter "d". This will write everything that has just happened into a file called "typescript". In the vi editor you can see that the file will be in windows format with carriage returns at the end of each line. You can remove these if you wish as explained in the article on how to use the vi editor.

"gimp" performs most of the functions of Photoshop. There are video editing programs but I am not familiar with them.

Most digital single lens reflex (DSLR) cameras can be set to produce either of two raw formats. A format that is proprietary to your brand of camera or DNG format, which most cameras can also produce. Unfortunately the DNG format does not include the camera settings used to take the picture. Most proprietary formats do. If you use your DSLR camera to take a picture in automatic mode, you may not remember what aperture and shutter speed was automatically selected. The program "exiftool" will handle most proprietary formats. If you used the proprietary format, and you have installed the program "exiftool", the following script will display the settings your camera used to take the picture. I named the script "camset".

# camera settings from raw file
echo f# speed iso
exiftool -T -aperture -shutterspeed -iso  $1

My camera is a Pentax camera, so it uses the PEF format. Following is an example of the use of the script to get information from my picture file named "IMGP0150.PEF".

./camset *0.PEF
f# speed iso
8.0     1/800   400

I have a new digital camera body that I use with old film camera lenses. The camera settings are recorded in the raw picture file even when the camera is set to the manual mode, if done properly. The lens aperture is not set on the lens. The lens is set to automatic. Then the aperture is set by the camera controls. When done this way, aperture, speed and iso are recorded in the picture file.

A DSLR camera can produce image files in jpeg format or raw format. You can install the program "dcraw", which converts raw still camera formats to ppm format, which can then be converted to jpeg with "pnmtojpeg". Dcraw works on DNG files and most proprietary raw formats. If there is a gray card in the scene, or a separate gray card shot taken at the same time, perfect color balance can be achieved if you follow the instructions in the dcraw man page.

Suppose you want to create "png" files representing only the ink on the stained and yellowed pages of an old manuscript or book. You use a DSLR camera and incandescent light to photograph the pages. You set the camera to save the images in raw DNG format or a proprietary format. Transfer the DNG files to your computer. Use dcraw to convert a typical page to ppm format. Use gimp to view the ppm version of the picture to see the coordinate numbers of the area you want to use as a color reference to make the pages white. Use dcraw to get the numbers needed to make the yellowed pages appear white. See the "man" page for dcraw to understand what you are doing. An example might be:

dcraw -v -A 1000 1000 5000 3000 page1.DNG
Write down the numbers that are needed to whiten the pages. Then use the numbers to convert all the DNG files of yellowed pages to ppm files of white pages:
dcraw -v -r 1.0 1.0327 2.293 1.037 *DNG
Then use gimp to see the left, top, right and bottom coordinates in the image that are beyond the page of the book and that you want to cut out of the image. But do not cut the image with gimp, use the script below for that. Use the following script to change all of the ppm files one at a time to png files:
# use netpbm to convert book page photo to png
# convert dng to ppm with dcraw
# eliminate lines between ppmtopgm and pnmtopng  
# add lines one at a time and view results with gimp
# divide text width by 6 to get pixels per inch
# cut between text and dark borders of image 
# pad way beyond what you need 
# cut for 1.5 inch left border, 8.5 inch page width
# 1 inch top border, 11 inch page height
# convert ppm to png one page at a time
# png file will print from gimp, not lpr
oldname=$1
newname=${oldname%.ppm}.png
echo "$newname"
ppmtopgm "$oldname" \
| pnmflip -cw \
| pnmrotate 0.6 \
| pnmnorm -bvalue 200 -wvalue 201 \
| pnmcut -left 500 -right 4500 -top 1100 -bottom 6300 \
| pnmpad -white -left=1000 -right=1000 -top=1000 -bottom=3000 \
| pnmcut -left 594 -width 4471 -top 822 -height 5851 \
| pnmtopng > "$newname"

You will need to consult the "man" pages for each of the commands in this script to understand how it works. You will need to use the early parts of this script to view the ppm files in gimp to see how to adjust the numbers. When the numbers are adjusted right then add the later parts of the script. The resulting png file can be printed to fit on a page from gimp or from the linux file viewer. It can also be printed from file viewers in Windows and in the Apple operating system. You can email it or post it on your website and others can print it.

DISASTER RECOVERY

A minor disaster you may want to recover from is if you start a long printout, and realize something is wrong and want to stop the printout. Enter "lpq" to see the job number of the printout, which might be 87. Then enter "cancel 87". Then enter "lpq" again and the print job should be removed from the list. This will stop sending any more pages to the printer. But the printer memory may already be full of pages that it has not yet printed. You may have to temporarily remove the power plug from the printer to erase the printer memory. One time the printing quit working because of an unknown software glitch. "Restart" would not fix it. I had to shut down completely and turn the computer back on.

Another disaster is when the screen freezes and nothing you do has any effect. Hold down the "ctrl" and "alt" keys, and tap the "F2" key. This should switch you to a black screen. Enter the user name "root", then the root password, then the command "shutdown -h now". This will shutdown the computer. Alternatively, you could enter "shutdown -r now", and the computer will shutdown and reboot.

Hard drives do not last forever. If boot up fails with a black screen requiring you to run "fsck", or if your personal files mysteriously become "read only" so you cannot write to them, your hard drive may be starting to wear out. Of course, a new hard drive will be blank, requiring new software installation. You need to back up personal files first. It is easy to replace a hard drive on a desktop machine with a full sized tower, not so easy on smaller machines. On a full sized tower you typically remove the side panel of the cabinet, unplug two connectors from the back of the hard drive, unscrew two screws holding in the hard drive, slide out the old hard drive and slide in the new one. Hard drives are a very small fraction of the cost of a new computer. Before you remove the old hard drive you may want to zero it out to protect private files. In the directory /dev see if sda or hda is listed. If so that is the name of your hard drive device. As superuser the command "dd if=/dev/zero of=/dev/sda" will zero your hard drive after a few minutes.

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