Linux File Systems

• /       root directory
• /bin     executable for single user mode
• /dev    devices that can be mounted by the system
• /etc  local configuration, administrative things
• /home home directories for most users
• /lib      shared libraries
• /mnt   mountable devices - temporary mount point for mountable devices
• /proc  kernel and process information
• /root   home of the superuser (root)
• /sbin   system binaries (executables)
• /tmp   temporary files
• /usr    lots of information used by the system
• /usr/lib    libraries that can be linked in C++ programs, like math (libm.a or libm.so)
• /usr/include    all the header files
• /var    variable data - files whose contents change at runtime

Linux Users

• There is one special user that has administrative powers - the superuser. It's name is root.
• Every user has a home directory that can be found under /home/username. They have an allocated disk space called the quota.
• The home directory contains configuration (resource) files that define their environment. They all start with a dot. Example: .signature.
• For example, the file ".cshrc" will always be executed whenever the user logs in or opens a terminal window.
• Each type of shell loads their own resource file. Example: .bashrc.

File Ownership and Permisions

• Every file belongs to a particular user, generally the creator of that file. This is the owner of the file.
• Users may be organized in groups and a group can have special permissions to a file.
• A file can be accessible for reading r, writing w, or executing x. To view the content of a directory, the directory should be executable.
• Usually the owner has read and write permission to a file, also execute permission if applicable. The root (su) had read and write permissions for any file (!!)
• The command ls -l displays the permissions of a file for the owner, the group, and everyone else (all).
• To change the permissions and ownership: chmod, chown.

Compressing Files

• The most common utilities for compressing and decompressing files on Linux are tar and gzip.
• The tar archiving utility allows us to compress several files into one archive and even whole directories at a time.
• Its name comes from tape archive.
• Options: cf for compressing, xf for decompressing.
• The gzip utility compresses one file at a time.
• Options: none to compress, -d to decompress.
• To archive more than one file, most people use a combination of tar and gzip in that order. Those archives have the extension .tar.gz or simply .tgz.