Linux file system

"On a UNIX system, everything is a file; if something is not a file, it is a process."

Sorts of files (on a Linux system)

Directories: files that are lists of other files. Special files: the mechanism used for input and output. Most special files are in /dev.

Links

Sockets and Named pipes: files are used to pass information between applications amongst other applications

The -l option to ls displays the file type

File types in a long list Symbol Meaning - Regular file d Directory l Link c Special file s Socket p Named pipe

File system layout

/

bin etcdevboot procmnt usrlibhome sbinrootopt vartmp

each subdirectory of root have special roles(By tradition):

/bin: executable commands

/sbin: sys adm commands

/etc: system configuration files

/lib shared libraries

/dev peripheral devices

/tmp temporary files

/mnt to mount external devices

/var Storage for all variable files and temporary files

created by users, such as log files

/proc system information

/usr/bin further exe files

/usr/sbin further system-important exe files

/usr/lib further libraries

User-installed programs typically go under the /usr/local hierarchy

The df command

[alaei@node65 ~]$ df -h

Using the df command with a dot (.) as an option shows the partition the current directory belongs to,

[alaei@node65 ~]$ df -h .

In a file system, a file is represented by an inode, a kind of serial number containing information about the actual data that makes up the file: to whomthis file belongs, and where is it located on the hard disk.

The file system in reality

use ls -i to disply indoe numbers

Orientation in the file system

The PATH environment variable lists those directories in the system where executable files can be found

[alaei@node65 ~]$ echo $PATH

The which command

Linux searches for required program in paths and as soon as a match is found, the search is stopped

The export command

The env command

Absolute and relative paths

A path, which is the way you need to follow in the tree structure to reach a given file, can be described as starting from the trunk of the tree (the / or root directory). In that case, the path starts with a slash and is called an absolute path

In the other case, the path doesn't start with a slash and confusion is possible between ~/bin/wc (in the user's home directory) and bin/wc in /usr. Paths that don't start with a slash are always relative. In relative paths we also use the . and .. indications for the current and the parent directory

~ means usr home directory

Manipulating files

more about ls

ls -l

ls -ltr

In most UNIX commands, options can be combined

Color ls default color scheme Color File type blue directories red compressed archives white text files pink images cyan links yellow devices green executables flashing red broken links

Crating and deleting files and directories

nautilus: The default file manager in Gnome, the GNU desktop.

konqueror: The file manager typically used on a KDE desktop.

mc: Midnight Commander, the Unix file manager

mkdir

mkdir -p : creating directories and subdirectories in one step

creating directories

[alaei@node65 ~]$ mkdir 1 2 5

[alaei@node65 ~]$ mkdir -p project/iut/1

Copying files with cp

-i, interactively prompt before overwriting files

-R, -r, --recursive copy directories recursively

Moving Files with mv mv can rename files or directories, or move them to different directories-f, force overwrite, even if target already

exists

-i, ask user interactively before overwriting files

Deleting Files with rm

-f, delete write-protected files without prompting-i, interactive ask the user before deleting files-r, recursively delete files and directories

There is no recycle bin in shell so s file is really gone when you use rm

Finding Files with locate The locate command is a simple and fast way to find files

The locate command searches a database of filenamesThe database needs to be updated regularly Usually this is done automatically with cron But locate will not find files created since the last update Options:-i option makes the search case-insensitive -r treats the pattern as a regular expression, rather than a simple string

Finding Files More Flexibly: find

find <path> name <searchstring>

[alaei@node65 ~]$ find . -name test

find . size +5000k[alaei@node65 ~]$

The grep command

The diff command

File Security

Owner

r w x

Group

r w x

Others

r w xd

.= filed= directoryl= link

File typeExecute

Write

Read

Each type of permission is assigned a access mode code:

read = 4 or r

write = 2 or w

execute = 1 or x

User group codes

user = u

group= g

others= o

The chmod command

The id command

Print information for USERNAME, or the current user.

Operation

+ add

- remove

= set exactly

Before: -rwxr-xr-x  archive.sh

Command: chmod o=r archive.sh

After: -rwxr-xr--  archive.sh

Before: -rw-r-----   topsecret.inf

Command: chmod g= topsecret.inf

After: -rw-------    topsecret.inf

Before: -rw-r--r--    publicity.html

Command: chmod og=rw publicity.html

After: -rw-rw-rw-   publicity.html

$ ls -l test_file

-rw-r--r-- 1 eric users

$ chmod o-r test_file

$ ls -l test_file

-rw-r----- 1 eric users

$ chmod g+wx test_file

$ ls -l test_file

-rw-rwx--- 1 eric users

$ chmod u=rw,g=r,o=r test_file

-rw-r--r-- 1 eric users

For changing file permissions in directory trees use -R .

$ chmod -R g-w test_dir

The permission numbers are determined by adding the values of the allowed permissions:

7 = read + write + execute

6 = read + write (but not execute)

5 = read + execute (but not write)

3 = write + execute (but not read)

4 = read (but not write and execute)

2 = write (but not read or execute)

1 = execute (but not read or write)

$ chmod 754 test_file

-rwxr-xr-x 1 eric users

Owner = 4 + 2 + 1 = 7

Group = 4 + 1 = 5

World = 4 = 4

The newgrp , chown and chgrp commands