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 / binetc dev bootproc mnt usrlib homesbinroot optvartmp

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 ~]$ df -h Using the df command with a dot (.) as an option shows the partition the current directory belongs to, ~]$ 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 whom this 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 ~]$ 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 ~]$ mkdir ~]$ 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 directorie s -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 filenames The 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 name ~]$ find. -name test find. size +5000k ~]$

The grep command The diff command

File Security Owner r w x Group r w x Others r w x d.= file d= directory l= link File type Execute 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 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 = = 7 Group = = 5 World = 4 = 4

The newgrp, chown and chgrp commands