Section 4

Managing Files and Filesystems

Copyright
Statement
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Introduction

The material in this section was initially written for the SCO OpenServer 5 operating system.  Much of the material also works on other Unix operating systems, although compatibility cannot be guaranteed, and no warranty for fitness is expressed or implied.

This section discusses UNIX filesystems, files, and directories.  The section discusses the components of filesystems - disk blocks, inodes, superblocks, and more.  The student is shown to create a filesystem, how to mount and unmount a filesystem, and much more.

Objectives

Upon completion of this section, students will be able to:

1.	Describe the structure of a UNIX filesystem
2.	Easily navigate a UNIX file system
3.	Identify the various file systems supported by SCO OpenServer 5, and their characteristics
4.	Identify different UNIX file types - ordinary files, directories, links, etc.
5.	Copy, move, and delete files and directories
6.	Create filesystems
7.	Mount and unmount filesystems
8.	Determine disk usage
9.	Effectively use file system management commands

Contents

1.	What is a hard disk drive?
2.	What is a filesystem?
3.	What is a "file"?
4.	What is a "directory"?
5.	Navigating the filesystem
6.	Understanding file and directory information
7.	How to create a filesystem
8.	How to mount a filesystem
9.	Commands for working with files and directories
10.	How full is a filesystem?
11.	How large is a directory tree?
12.	How to find files and directories
13.	How to check and fix a damaged filesystem
14.	What is the "/lost+found" directory?
15.	Problem: Out of inodes
16.	Problem: System reporting "Unrecoverable error reading SCSI disk"
17.	Miscellaneous filesystem administration commands

An exploded view of a hard disk drive

     (Figure courtesy of SCO.  SCO OpenServer Handbook, p. 296)

Number of Megabytes =  (No. of Cylinders) * (No. of heads) * (Sectors per track) * 512 
						1024 * 1024

1.	What is a hard disk drive?

Computer applications and data are magnetically stored on a hard disk drive so they can be accessed at any time.  When a computer is properly shut down, this information is saved on the disk drive, and is available again when the computer is restarted.

Physically, a hard disk drive consists of one or more disk platters.  These disk platters are divided into cylinders, tracks, and sectors.

Platters	Usually an aluminum-coated disk with an "oxide" or "thin film" media where the data is actually stored.	

Tracks	
Concentric rings on each platter where the data is stored magnetically.	

Read/Write Heads	
Usually one read/write head per platter surface, i.e., one head on the top of each platter, and one head on the bottom of each platter.  All of the heads of a hard disk drive usually move in unison.	

Sectors	
Each track is broken down into smaller units named sectors.  Each sector contains 512 bytes of data.  On a hard drive you'll usually see a number that defines the number of sectors per track - 32, 64, etc.	

Spindle	
The cylindrical object (or drum) that goes through the middle of each platter.  The platters spin around the spindle similar to the way that an automobile tire spins on an axle.	

Cylinders	
The set of all tracks (on all platters) that are the same distance from the spindle.	

2.	What is a filesystem?

UNIX computer systems store data on disk drives using a structure called a filesystem.  Quoting SCO, a filesystem is a distinct division of the operating system, consisting of files, directories, and the information needed to access and locate them.

There are many different types of filesystems.  In general, improvements have been made to filesystems with new releases of operating systems, and each new filesystem has been given a different name.

•	UNIX filesystems store information in a hierarchy of directories and files.

•	A filesystem is created when a disk is formatted with the proper UNIX utilities/commands.

•	These are the names of some common filesystems supported by SCO OpenServer 5:

HTFS	High Throughput Filesystem (default)	
DTFS	Desktop Filesystem	
EAFS	Extended Acer Fast Filesystem	
AFS	Acer Fast Filesystem	
S51K	AT&T UNIX System V 1KB Filesystem	
HS	High Sierra CD-ROM Filesystem	
ISO9600	ISO 9600 CD-ROM Filesystem	
XENIX	XENIX Filesystem	
DOS	DOS Filesystem	
Rockridge	Rockridge CD-ROM Filesystem	

A few differences between filesystems

	Long 
Filenames	Bootable	Max. Inodes	
HTFS	yes	no	227	
DTFS	yes	no	231	
EAFS	yes	yes	216	
AFS	no	yes	216	
S51K	no	yes	216	
XENIX	no	yes	216	

	A.	The "Hierarchical" Filesystem Structure

The UNIX filesystem lets users group files together in a logical and efficient manner by organizing them like folders inside a file cabinet.

	i.	The UNIX File System Structure

The entire UNIX filesystem is a hierarchical organization of files and directories.  It is logically organized into meaningful directories, with each directory containing files and additional sub-directories.

The top level of the UNIX filesystem is symbolized by the "/" character. Being in this directory is like looking at a series of file cabinets against a wall.  This directory has a special name - it is called the "root" directory.

"root"
Directory		This is the very top level of the file system.  It is symbolized by the "/" character.	

The root directory has many sub-directories.  The most important sub-directories are named "bin", "dev", "etc", "opt", "stand", and "usr".  There's also usually a "home" or "u" directory.

B.	The "root" Directory

The SCO OpenServer 5 root directory contains the following system directories:

/bin	UNIX Commands	
/dev	Device special directory	
/etc	Additional programs and data files	
/lib	C programming library directory	
/mnt	Mount directory; usually reserved for mounting filesystems	
/opt	Location of shared software storage objects (SSO's)	
/shlib	Shared libraries	
/stand	Contains the kernel (unix) and boot files, including the loader (boot)	
/tcb	The Trusted Computing Base security binaries and databases	
/tmp	Temporary directory	
/usr	User routines	
/var	Non-shared software storage object files	

C.	Detailed Components of a Disk Filesystem

Although the details will vary between UNIX file system types (AFS, DTFS, EAFS, HTFS, etc.), the following items are generic file system components:

Boot Block	
•	Stores boot procedures	

Super Block	
•	Contains file system size and status
•	Inode information (total number allocated, total free, free inode number)
•	One copy in memory, one copy on disk	

Inode Table	
•	Type and permissions
•	Hard link count
•	UID of owner
•	GID of owner
•	size in bytes
•	date and time stamps (creation, last accessed, last modified)
•	Disk block addresses	

Storage Blocks	
•	Data blocks
•	Regular files - file contents
•	Directory files - filenames and inode numbers	

A UNIX file is just a string of bytes:

0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	
T	h	i	s		i	s		a		f	i	l	e	.	

3.	What is a "file"?

A.	The Concept of a "File"

In the most strict definition, a file is a string of bytes that has been assigned to a directory.

Conceptually, a UNIX file is like a document in a file folder in a file cabinet.  However, unlike a paper document, a file can store all types of information, from (a) a simple memo, to (b) payroll data, to (c) a document that contains text, graphics, sound, and video.

i.	Length of filenames

The length of a filename may be limited to 14 characters with some filesystems, while it may be 255 characters with a different filesystem.  Limits for SCO filesystems will be presented later in this section.

ii.	Valid file name characters

A file name can consist of any alphabetic character, any numeric character, underscores (_), and periods (.).  Do not use blank spaces in file names.  Do not use the following characters in filenames:

! " ` ' ;  /  \  $  *  &  <  >  (  ) | { } [ ] ~

If you could view the contents of a directory file …

1643	group	
259	inittab	
18483	passwd	
382	rc2.d	
41906	issue	

4.	What is a "directory"?

A.	The Concept of a "Directory"

In a strict technical sense, directories act as a table of contents.  If you could look inside of a directory file, you would see two columns of information -- file inode numbers and file names.

Directories are very similar to both file folders and drawers within file cabinets.  For instance, for a client that you do business with, you may have a file folder named "Acme, Inc.".  This folder may contain a number of documents that show your relationship with Acme - invoices, bills paid, letters, etc.

On the UNIX system, you might create a corresponding directory that contains all of your files for "Acme".  Again, this name can include letters, spreadsheets, and other documents.

Directory		Conceptually, directories are like drawers and file folders within a file cabinet.	

What happens …

cd /usr/spool/lp/admins

cd /u*/s*/l*/a*

cd -

cd

5.	Navigating the Filesystem

A.	Simple File System Navigation

When navigating a UNIX filesystem, there is one primary command for moving around the filesystem ("cd"), and another command that tells you where you are currently located ("pwd").  "cd" stands for change directory, and "pwd" stands for print working directory.  A third primary command, "ls", lists the files and directories that are contained within each directory.

i.	Moving Around the Filesystem

  cd										

"cd" stands for change directory.  It is the primary command for moving you around the filesystem.

cd /usr
Moves you to the "/usr" directory.  "/usr" becomes your current working directory.

cd /usr/fred
Moves you to the "/usr/fred" directory.

Absolute Path		An absolute path always begins with a "/".  This indicates that the path starts at the root directory.  An example of an absolute path is "/usr/bin".

Relative Path		A relative path does not begin with a "/".  It identifies a location relative to your current position.

An example of a relative path is this cd command:

cd ../../bin

cd /u*/f*
Moves you to the "/usr/fred" directory if this is the only directory matching this wildcard pattern.

cd
Issuing the "cd" command without any arguments moves you to your home directory.

cd -
Using the Korn shell, this command moves you back to your previous working directory.  This is very useful when you're in the middle of a project, and keep moving back-and-forth between two directories.

ii.	Displaying the Current Directory

  pwd										

"pwd" stands for print working directory.  It displays your current position in the UNIX filesystem.

pwd
There are no options (or arguments) with the "pwd" command.  It is simply used to report your current working directory.

What happens …

ls -al /usr

ls -alR /usr

ls -ld /usr

iii.	Listing File Information

  ls										

"ls" stands for list.  It is used to list information about files and directories.

ls
This is the basic "ls" command, with no options.  It lists the files in your current working directory.  Filenames beginning with a decimal are considered hidden files, and they are not shown.

ls -a
The -a option tells the ls command to report information about all files, including hidden files.

ls -l
The -l option tells the ls command to provide a "long listing" of information about the files and directories it reports.  The long listing will provide important information about file permissions, user and group ownership, file size, and creation date.

ls -al
This command provides a long listing of information about all files in the current directory.  It combines the functionality of the -a and -l options.

ls -al /usr
This command lists long information about all files in the "/usr" directory.

ls -alR /usr | more
This command lists long information about all files in the "/usr" directory, and all sub-directories of /usr.  The -R option tells the ls command to provide a recursive listing.

ls -ld /usr
Rather than list the files contained in the /usr directory, this command lists information about the /usr directory itself (without generating a listing of the contents of /usr).  This is very useful when you want to check the permissions of the directory, and not the files it contains.

Exercise 4-1:   Moving Around the Filesystem

Step #1	Log into the computer system.

Step #2	Type "pwd" to display your current working directory.  What does it display?

Step #3	Type "cd /".  What happens?

Step #4	Type "pwd" to display your current working directory.  What does it display now?

Step #5	Type "cd /usr".  What happens?

Step #6	Type "pwd" again.  What is displayed?

Step #7	Type "cd lib".  Notice this does not begin with a "/" character.  Where do you think you are now located?

Step #8	Type "pwd".  Where are you now located?

Step #9	Type "cd".

Step #10	Type "pwd".  Where are you now located?

Exercise 4-2:   Listing Files and Directories

Step #1	Type "pwd" to display your current working directory.  What does it display?

Step #2	Type "ls".  This generates a simple listing of the files and directories in your current directory.

Step #3	Type "ls -al".  This will generate a long listing of all of the files in your current directory.

Step #4	Type "cd /".

Step #5	Type "pwd" to display your current working directory.  You should be in the "root" directory.

Step #6	Type "ls".  What is displayed?

Step #7	Type "ls -al".  What is displayed now?

Step #8	Type "cd /usr".

Step #9	Type "pwd" again.  Your should be in the "/usr" directory.

Step #10	Type "ls -al".  What is displayed?

Step #11	Type "cd".

Step #12	Type "pwd".  You should now be in your "home" directory.

A sample directory listing

drwxr-xr-x  2 root     sys        60676 Aug 22  1994 Lib
-r--r--r--  1 root     sys        60676 Aug 22  1994 README
drwxr-xr-x  2 root     sys        60676 Aug 22  1994 Source
-rwxr-xr-x  2 root     sys        60676 Aug 22  1994 gzexe
-rwxr-xr-x  2 root     sys        60676 Aug 22  1994 gzip        
-rwxr-xr-x  1 bin      bin       242436 Feb 20 16:07 httpd
-rwsr-xr-x  1 uucp     uucp      599604 Sep 22  1995 kermit      
-rwxr-x--x  1 root     sys       171195 Jan 22 12:15 memhog      
-rwxr-x--x  1 root     sys         5599 Jan 22 12:15 nlsym       
-rwxr-xr-x  2 root     sys       553836 Feb 20 16:40 perl     
-rwxr-xr-x  2 root     sys       553836 Feb 20 16:40 perl5.003
-rwxr-xr-x  1 root     sys        13855 Feb 20 16:40 perlbug   
-rwxr-xr-x  1 root     sys         8984 Feb 20 16:40 perldoc    
drwxr-xr-x  2 root     sys        60676 Aug 22  1994 src
-rwxr-x--x  1 root     sys       108781 Jan 22 12:15 u386mon

6.	Understanding File and Directory Information

A.	Understanding File Type Information

Understanding file information -- especially the output of the "ls -al" command -- is very important.

On each line of output from the "ls -al" command, the first ten characters of output can be broken down as follows:

File
Type	
User	
Group	
Other	
d	r	w	x	r	w	x	r	w	x	
d	r	w	x	r	w	-	r	-	-	
-	r	w	x	r	-	-	r	-	-	
-	r	-	x	-	-	-	-	-	-	

File Type:	The character in the first column indicates the “type” of file that is listed on the current line.  This first character is usually a "-" (indicating an ordinary file) or a "d" (indicating a directory).

User:	This field contains information about permissions for the owner of the file or directory.

Group:	This field contains information about permissions for users in the same group as the owner of the file or directory.

Other:	This field contains information about permissions for users not in the same group as the owner of the file or directory.

Possible UNIX File Types

File Type	Description	
-	Indicates a file	
d	Indicates a plain directory	
b	A block special file	
c	A character special file	
l	A link	
m	Shared memory	
p	A named pipe	
s	A semaphore	

Regular file (-)	
•	No imposed structure on the internal contents - just a string of bytes
•	ASCII text or binary data	

Directory File (d)	
•	A "table of contents" file
•	Has a defined internal structure
•	Provides file system organization	

Block Special File (b)	
•	Identifies a device
•	Block I/O
•	Floppy disks, hard disks, tape devices	

Character Special File (c )	
•	Identifies a device
•	Character I/O
•	Serial ports, parallel ports (terminals, printers)	
Symbolic Link (l)	
•	A file that point to another file
•	Used to provide an alias for another file	

Shared Memory (m)	
•	Allows multiple programs to access a common memory space
•	Used most often by application programs	

Named Pipe (p)	
•	Used to pass data between processes	

Semaphore (s)	
•	Used to synchronize concurrently running processes
•	Used by application programs	

B.	Understanding File/Directory Permissions  (Access Control)

Column 1	Columns 2-4	Columns 5-7	Columns 6-8	
d	r	w	x	r	w	x	r	w	x	
d	r	w	x	r	w	-	r	-	-	
-	r	w	x	r	-	-	r	-	-	
-	r	-	x	-	-	-	-	-	-	

Column 1:	Shows whether the file is a directory (d), ordinary file (-), or other file type.

Columns 2-4:	Shows the file permissions for the user who owns the file (user).  Permissions can be read (r), write (w), and execute (x).

Columns 5-7:	Shows the file permissions for the group the file is owned by (group).  Permissions can be read (r), write (w), and execute (x).

Columns 8-10:	Shows the file permissions for persons not in the owner's group (others).  Permissions can be read (r), write (w), and execute (x).

Other fields in the "ls -al" output

         Links               Size in Bytes
            |        Group         |                File Name
            | Owner     |          |       Date        |
            |  |        |          |      /    \       |
            |  |        |          |     /      \      |

drwxr-xr-x  2 root     sys        60676 Aug 22  1994 Lib
-r--r--r--  1 root     sys        60676 Aug 22  1994 README
drwxr-xr-x  2 root     sys        60676 Aug 22  1994 Source
-rwxr-xr-x  2 root     sys        60676 Aug 22  1994 gzexe
-rwxr-xr-x  2 root     sys        60676 Aug 22  1994 gzip        
-rwxr-xr-x  1 bin      bin       242436 Feb 20 16:07 httpd
-rwsr-xr-x  1 uucp     uucp      599604 Sep 22  1995 kermit      
-rwxr-x--x  1 root     sys       171195 Jan 22 12:15 memhog      
-rwxr-x--x  1 root     sys         5599 Jan 22 12:15 nlsym       
-rwxr-xr-x  2 root     sys       553836 Feb 20 16:40 perl     
-rwxr-xr-x  2 root     sys       553836 Feb 20 16:40 perl5.003
-rwxr-xr-x  1 root     sys        13855 Feb 20 16:40 perlbug   
-rwxr-xr-x  1 root     sys         8984 Feb 20 16:40 perldoc    
drwxr-xr-x  2 root     sys        60676 Aug 22  1994 src
-rwxr-x--x  1 root     sys       108781 Jan 22 12:15 u386mon

C.	Understanding Other Field Information

The other fields of output information from the ls -al command are as follows:

Links	
•	By how many names is this file known?	

Owner	
•	The user who "owns" this file	

Group	
•	The group that the owner belongs to	

Size in Bytes	
•	The size of the file in bytes	

Date	
•	Unless one of the -c or -u options is specified, the modification time refers only to changes made to the file's data, or the creation of the file.	

File name	
•	The name of the file
•	The file name is contained in the directory 	

7.	How to create a filesystem

Creating a filesystem on a disk drive using OpenServer 5 is very simple.  

While creating a filesystem on a hard disk is a little more complicated than creating a filesystem on a floppy disk, the procedures are very similar.  As a sample exercise, follow this step-by-step procedure to create a filesystem on a diskette:

1.	Log in as the root user.
2.	Insert a floppy disk into the floppy disk drive holder.
3.	At the Unix command line type  mkdev fd
4.	Select  1. Filesystem
5.	Select the following option:

4. 135tpi, double sided, 18 sectors per track 
   (1.44Mb 3.5 inch)
6.	Press the <Enter> key when prompted.
7.	Enter y to format the floppy disk first.  

The system will report the tracks and heads it is formatting as it formats the floppy.  After formatting the floppy disk, it will perform a verification process.
8.	Next you are prompted to use the default filesystem type.  Enter n so you can view the other filesystem options available.
9.	After viewing the available options, select the HTFS filesystem type. (Note - you must enter the type using upper-case characters.)
10.	The floppy filesystem is created and checked for you.  Press <Enter> to return to the previous menu, then enter q to quit.

Mounting a diskette filesystem

8.	How to mount a filesystem

Before a filesystem can be used it must be mounted.

Here is the step-by-step procedure to mount the diskette filesystem just created in the previous exercise:

1.	Log in as the root user.
2.	Make sure the floppy diskette is in the floppy disk drive.
3.	Assuming you created an HTFS filesystem on the diskette, and the diskette drive is the first floppy drive on your computer system, enter this command to mount the diskette filesystem onto your local filesystem:

		mount /dev/fd0 /mnt
4.	Type the following command.  The diskette filesystem should now appear as a mounted 1.44 MB filesystem:

		df -kv
5.	You can now access the diskette filesystem with the usual Unix filesystem commands:

		cd /mnt
		ls -al
		cd /  
6.	When you are finished using the diskette, you should unmount it.  This is done with the umount command:

		umount /mnt

Other useful commands:	dtype, fstyp

9.	Commands for Working with Files and Directories

A.	Viewing Text Files

 cat										

The “cat” command lets you view text files.  “cat” stands for concatenate.

cat /etc/passwd
This command displays the “/etc/passwd” file on your screen.

cat /etc/profile
This command displays the “/etc/profile” file on your screen.  Notice that some of the contents of this file may scroll off of your screen.

The drawback of the “cat” command is that the contents of the file may scroll off of the screen.  Therefore, the “more” command is usually more useful for this purpose.

B.	Viewing Text Files in a Controlled Manner

 more										

The “more” command lets you view text files.  It displays files one screenful at a time.

more /etc/passwd
This command displays the /etc/passwd file one screenful at a time.

When using the more command, you can use several commands to view the text file.  These commands are shown below:

Table 5-4:	Options available within the “more” command.

Command	Meaning	
<spacebar>	Display the next screen of information	
<Enter>	Display one more line of information	
q	“quit” the more command	

C.	Searching for Text Strings in Files

 grep										

Think of the “grep” command as a “search” command.  It is used to search for text strings within one or more files.

grep ‘stu’ /etc/passwd
This command searches for all occurrences of the text string ‘stu’ within the “/etc/passwd” file.  It will find and print (on the screen) all of the lines in this file that contain the text string ‘stu’.

grep ‘stu1’ /etc/passwd
This command searches for all occurrences of the text string ‘stu1’ within the “/etc/passwd” file.  Notice how it differs from the previous command.

grep ‘joe’ *
This command searches for all occurrences of the text string ‘joe’ within all files of the current directory.

	You can use the “grep” command to find a file when you can’t remember the filename but you know some of the text that is in the file.	

D.	Copying, Moving, and Deleting Files and Directories

i.	Copying Files and Directories

 cp										

The “cp” command is used to copy both files and directories.

cp .profile .profile.bak
This command copies your “.profile” to a file named “.profile.bak”.  You now have a backup copy of your original file.

cp /usr/fred/Chapter1 .
This command copies the “Chapter1” file in “/usr/fred” to the current directory.

cp /usr/fred/Chapter1 /usr/mary
This command copies the “Chapter1” file in “/usr/fred” to the directory named “/usr/mary”.

ii.	Moving and Renaming Files

 mv									

The “mv” command is used to move and rename files.

mv Chapter1 Chapter1.bad
This command renames the file “Chapter1” to the new name “Chapter1.bad”.

mv Chapter1 garbage
This command renames the file “Chapter1” to the new name “garbage”.  (Notice that if “garbage” is a directory, “Chapter1” would be moved into that directory).

mv Chapter1 /usr/fred/tmp
This command moves the file “Chapter1” into the directory named “/usr/fred/tmp”.

iii.	Deleting Files and Directories

 rm										

The “rm” command is used to remove files and directories.  (Be very careful when removing files and directories!)

rm Chapter1.bad
This command deletes the file named “Chapter1.bad”.

rm Chapter1 Chapter2 Chapter3
This command deletes the files named “Chapter1”, “Chapter2”, and “Chapter3”.

rm -r new-novel
This command deletes the directory named “new-novel”.  This directory, and all of its’ contents, are erased from the disk, including any sub-directories and files.  

WARNING!	
BE VERY CAREFUL 
WITH THIS COMMAND !	

rmdir new-novel
This command also deletes the directory named “new-novel”.  However, if the directory is not empty, the “rmdir” command will not remove it.  It will write a warning message to your screen instead.  THIS IS SAFER THAN THE “rm -r” COMMAND AND IS RECOMMENDED.

E.	Creating and Removing Directories

i.	Creating New Directories

 mkdir									

The “mkdir” command is used to create new directories (sub-directories).

mkdir tmp
This command creates a new directory named “tmp” in your current directory.

mkdir /usr/fred/tmp
This command creates a new directory named “tmp” in the directory “/usr/fred”.  “tmp” is now a sub-directory of “/usr/fred”.

mkdir -p /home/joe/customer/kroger
This command creates a new directory named /home/joe/customer/kroger, and creates any intermediate directories that are needed.  If only /home/joe existed to begin with, then the directory "customer" is created, and the directory "kroger" is created inside of customer.

ii.	Removing Directories

 rm, rmdir									

The “rm” and “rmdir” commands are used to remove directories.  (Be very careful when removing directories!)

rm -r new-novel
This command deletes the directory named “new-novel”.  This directory, and all of its’ contents, are erased from the disk, including any sub-directories and files.

WARNING!	
BE VERY CAREFUL 
WITH THIS COMMAND !	

rmdir new-novel
This command also deletes the directory named “new-novel”.  However, if the directory is not empty, the “rmdir” command will not remove it.  It will write a warning message to your screen instead.  THIS IS SAFER THAN THE “rm -r” COMMAND AND IS RECOMMENDED.

F.	Creating Archives with the "tar" Command

The tar ("tape archive") command can be used to create archives on magnetic tapes.  It can also be used to create general-purpose archives that can be transferred across filesystems, networks, and the Internet.

 tar										

tar cvf /dev/rct0 /home
This command writes a tar archive to the tape device /dev/rct0.  It copies the files in the /home directory, and all subdirectories of /home.

tar cvf /dev/fd0 /home/fred
This command writes a tar archive to the diskette device /dev/fd0.  It copies the files in the /home/fred directory, and all subdirectories of /home/fred.

tar cvf /tmp/home.tar /home
This command writes a tar archive to a file named /tmp/home.tar.  It copies the files in the /home directory, and all subdirectories of /home.

G.	Compressing Files

UNIX includes the compress command to shrink files.  This helps save disk space, and reduces file transfer times when transmitting files across networks or slow data communication lines.

 compress									

compress /tmp/home.tar
this command compresses the file /tmp/home.tar, and replaces it with a file named /tmp/home.tar.Z.

H.	Miscellaneous Commands

i.	Counting Characters, Words, and Lines

 wc										

The “wc” command stands for “word count”.  It counts the number of characters, words, and lines that are contained in a text stream.

The wc command

/> wc -l /etc/passwd             
     26 passwd                 

/> wc /etc/passwd                
     26     65   1306 passwd   

The file command

/bin> file c*                                  
cat:            ELF 32-bit LSB executable 80386
cd:             sh commands text               
chgrp:          ELF 32-bit LSB executable 80386
chmod:          ELF 32-bit LSB executable 80386
chown:          ELF 32-bit LSB executable 80386
chroot:         ELF 32-bit LSB executable 80386
cksum:          ELF 32-bit LSB executable 80386
clear:          Bourne/Korn shell commands text

wc /etc/passwd
This command tells you the number of characters, words, and lines in the /etc/passwd file.

wc -l /etc/passwd
This command tells you the number of lines (only) in the /etc/passwd file.

ii.	Determining a File's Type

 file										

The “file” command shows you information about the file type - whether the file is text, machine language, etc.

file *
This command tells you information about every file in the current directory.

file /etc/*
This command tells you information about every file in the /etc directory.

10.	How full is a filesystem?

Filesystems have limited space and if not properly maintained, will eventually become full with continued use.

You can tell how full a filesystem is by using the df and dfspace (specific to SCO) commands. 

  df												

"df" stands for disk free.  This command is used to show the amount of free space on one or more filesystems.

df
A basic display of the free disk space (showing blocks and i-nodes) on all mounted filesystems.

df /
Displays the free disk space in the / filesystem.

df -kvi
A more verbose display showing the free disk space of all filesystems, measured in kilobytes and i-nodes.

Several views of the same filesystem

/> df                                                                          
/         (/dev/root        ):   588280 blocks   230035 i-nodes                
/stand    (/dev/boot        ):    23984 blocks     4992 i-nodes                
/usr/lib/ssl/CD (/dev/cd0         ):    42000 blocks    38829 i-nodes          

/> df -kvi                                                                     
Mount Dir  Filesystem           blocks   used   free %used iused ifree %iused  
/          /dev/root            1156688 862548 294140  75%  59141 230035   21% 
/stand     /dev/boot             20000   8008  11992  41%     16  4992    1%   
/usr/lib/s /dev/cd0             629001 608001  21000  97%  26659 38829   41%   

/> dfspace                                                                     
/         :     Disk space: 287.24 MB of 1129.57 MB available (25.43%).        
/stand    :     Disk space:  11.71 MB of  19.53 MB available (59.96%).         
/usr/lib/ssl/CD :       Disk space:  20.50 MB of 614.25 MB available ( 3.34%). 
                                                                               
Total Disk Space: 319.46 MB of 1763.36 MB available (18.12%).

  dfspace											

"dfspace" is a command specific to SCO Unix systems.  It provides a view of the free space on one or more filesystems that is easier to read.

dfspace
The dfspace command formats the output for the df command to make it easier to read.

11.	How large is a directory tree?

At times it may be necessary to know how large a directory tree is on a Unix system.  This is easily accomplished with the du command.

  du												

"du" stands for disk usage.  This command is used to show the amount of disk space consumed by one or more directories.

du
Shows the disk usage of the current working directory.  Each file in the directory and it's usage (in blocks) is displayed.

du -k
Shows the usage of the current directory in 1024-byte units (kilobytes).

du /home/fred
Shows the disk usage of the /home/fred subdirectory.

du -ks /home/fred
Shows only a summary the disk usage of the /home/fred subdirectory.

du -ks /home/fred/*
Shows a summary of each subdirectory of /home/fred.

Syntax of the find command

Basic syntax:

	find <path-names> <search criteria>

A few sample commands:

	find / -name ls -print

	find /home /usr/local -name "lostfile" -print

	find /home -type f -exec grep -il "peanut butter" {} \;

12.	How to find files and directories

It is often necessary to be able to find files or directories on a UNIX system.  Some times it is necessary to search for a file by name; other times only a partial filename or other information is available.  In all cases, the UNIX find command can be used to find a file by name, partial name, size, date, permissions, ownership, or many other search criteria.

The find command lets you search for files using a wide variety of search criteria.  

 find										

The find command is very powerful.  It can search the entire filesystem for one or more files that you specify to look for.  This is very helpful when a file has been “lost”.

find / -name Chapter1 -type f -print
This command searches through the root filesystem (“/”) for the file named “Chapter1”.  If it finds the file, it prints the location to the screen.

find /usr -name Chapter1 -type f -print
This command searches through the “/usr” directory for the file named “Chapter1”.

find /usr -name “Chapter*” -type f -print
This command searches through the “/usr” directory for files that begin with the letters “Chapter”.  The filename can end with any other combination of characters.

This will match filenames such as “Chapter”, “Chapter1”, “Chapter1.bad”, “Chapter_in_life”.

find /usr -name “*memo*” -type f -print
This command searches through the “/usr” directory for files that contain the letters “memo”.  

Running the fsck command

/> fsck /dev/fd0                 
                                 
  /dev/fd0                       
  Fast File System:  Volume:     
                                 
  NO PARTIAL TRANSACTIONS PENDING
  3 files 36 blocks 2794 free

13.	How to check and fix a damaged filesystem

Occasionally UNIX filesystems can become corrupt if the system is shut down improperly, or if the disk suffers from some type of minor failure.  In these events, it may be necessary to try to repair the filesystem.

UNIX filesystems are repaired using the fsck (file system check) command.

 fsck										

The fsck command is used to try to fix filesystems that have suffered some type of failure.

fsck /dev/fd0
This command checks the filesystem corresponding to the device /dev/fd0.  This device refers to the first floppy disk on a UNIX system.

Note:  It is sometimes helpful to run the fsstat command before running fsck.  The fsstat command can tell you if a filesystem needs cleaning.

14.	What is the "/lost+found" directory?

•	A lost+found directory is automatically created in a filesystem by mkdev fs when a new filesystem is created.  (mkdev fs is run automatically when you run mkdev hd)
•	In Phase 3 of it's filesystem checking process, the fsck command will place valid but unreferenced files in the lost+found directory.
•	The fsck command does not create or extend the lost+found directory!  The directory must already exist, and it must contain a sufficient number of empty slots in the directory for use by fsck.

15.	Problem:  "Out of inodes" error on a filesystem

Running out of inodes on a filesystem is a very serious error.  Until the problem is corrected users will not be able to create new files on this filesystem.  

When an SCO OpenServer 5 filesystem runs out of inodes you'll receive the following error message:

NOTICE: type: Out of inodes on type dev hd (major/minor)

Warning:

	The only way to fix this problem is to remove unnecessary files from the filesystem.	

The only way to increase the number of inodes on most filesystems is to (1) backup your data, (2) unmount the filesystem, and (3) run mkfs on the filesystem, increasing the desired number of inodes on the filesystem.  This procedure will destroy any data currently on the filesystem; therefore the data must be restored from the backup tape.

 

When bad things happen to good disks

	NOTICE: Sdsk: Unrecoverable error reading SCSI disk 1 dev 1/64
			(ha=0 id=0 lun=0) block=194091
			Medium error: Unrecovered read error

16.	Problem:  "Unrecoverable error reading SCSI disk" errors

This message is reported by SCSI disks if a hard disk develops a bad track after the system is installed and running.

If this type of error occurs, use the badtrk command to create a new bad track table to the system can avoid the new bad track(s).

To run badtrk, follow these steps:

1.	Reboot the system and enter single-user mode.  Do not use shutdown su to do this.
2.	Run badtrk, scan the disk and the entire UNIX partition.  A thorough scan is recommended if new bad tracks have appeared.  
3.	Select nondestructive mode to preserve the data on your hard disk.
4.	When the scan completes, quit badtrk, and return the system to multi-user mode.

17.	Miscellaneous Filesystem Administration Commands

i.	Determining a Filesystem's Type

 fstyp									

The fstyp command lets the superuser determine a filesystem's type (HTFS, DTFS, EAFS, AFS, etc.) using heuristic programs.

fstyp /dev/root
This command tells you the type of filesystem installed on the device /dev/root.

ii.	Determining a Disk's Type

 dtype									

The dtype command determines a disk's type.  Besides reporting on filesystems, it can also report if the device contains a tar or cpio archive, along with other information.

dtype /dev/root
This command tells you the type of filesystem installed on the device /dev/root.

dtype /dev/fd0
This command tells you the type of filesystem installed on the device /dev/fd0.

iii.	Determining if a Filesystem Needs Cleaning

 fsstat									

The fsstat command is used to determine if a filesystem needs cleaning.  It is often used before using fsck.

fsstat /dev/fd0
This command reports whether the filesystem referred to by /dev/root requires cleaning with fsck.

iv.	Identifying processes using a file or filesystem

 fuser									

The fuser command can be used to help you determine if a file or filesystem is being used by a user or process.

fuser -u /tmp
This command reports the PID's and usernames of any processes currently using the /tmp filesystem.

 
Managing Files and Filesystems - Final Exam

1.	The command used to generate a long listing of all files in the /usr/bin directory is:
2.	The command used to find a file somewhere in the /home or /usr/local filesystems that contains the text string "gross sales" is:
3.	The following command takes you to what directory on a SCO OpenServer 5 system?

			cd /u*/s*/l*/a*/l*/i*

4.	You mount a CD-ROM with an EAFS filesystem with this command (hint: remember that a CD-ROM is a read-only filesystem):
5.	Where is the actual ls command located on a SCO OpenServer 5 computer system?
6.	What is the primary command used on Unix computer systems to check and repair filesystems?
7.	You've taken up a career as a spy, and you need to create a tar backup of a directory named /usr/local/secrets.  The backup will fit on a 3.5" 1.44MB floppy - the second floppy drive in the computer system.  What command will you issue to create this tar archive?
8.	In the last question we were wrong - the tar archive won't fit on one diskette, and you only have one diskette at your disposal.  However, you can still accomplish the job if you compress the archive first, and then copy the compressed archive to diskette.  What are the steps you need to take to get this data on the floppy?

9.	You have a filesystem named /critical_data that you need to unmount.  However, the umount command keeps failing, saying that the filesystem is busy.  How do you determine what user or process is using this filesystem?
10.	A computer virus was placed onto your computer system between 8 a.m. and 9 a.m. this morning, and you just received an e-mail from a hacker demanding ransom before the virus attacks.  You have less than five minutes.  How do you find and remove this virus?
11.	What percentage of space is used on your root filesystem?
12.	What percentage of inodes are used on your root filesystem?
13.	How many files are in the /usr/bin directory?  What is the easiest way to determine this value?
14.	What is the size of the /opt/K/SCO/Unix/5*/usr directory in megabytes?
15.	How do you create a listing of the files in the /bin directory so that the largest file is shown at the top of the listing?