- Pathnames consist of file/directory names, separated by slashes (as opposed to sloshes)
- Absolute and relative file names
- Absolute to the root (start with slash)
- Relative to the current working directory
- UNIX philosophy: Everything is a file
- Plain file
- Directory
- Block device (disk, CD, DVD, tape)
- Character device (keyboard, mouse, modem)
- Socket link (internet)
- FIFO (pipes between processes)
- Symbolic link (aliases, shortcuts)
- File systems
- Root file system
- Mounted file systems
- /mnt and /media
- Local and NFS
- mount command
- df command
- Each node has a number of attributes:
- Name
- Type
- Size
- Owner
- Group (each file belongs to one group, even if the owner belongs to multiple groups)
- Permissions
- Number of links
- Access dates
- ls -l gives a full listing
geoff@sherman:UNIXUse> which ls ls: aliased to ls -F geoff@sherman:UNIXUse> ls -la total 48 drwxr-xr-x 4 geoff www 512 Dec 30 15:17 ./ drwxr-xr-x 8 geoff www 512 Dec 30 14:10 ../ -rw-r--r-- 1 geoff www 3084 Dec 30 15:17 FileSystem.shtml -rw-r--r-- 1 geoff www 4551 Dec 30 12:06 History.shtml -rw-r--r-- 1 geoff www 751 Dec 30 14:13 Mastery.shtml drwxr-xr-x 2 geoff www 512 Dec 30 13:46 MyCode/ drwxr-xr-x 2 geoff www 512 Dec 30 13:01 Pictures/ -rw-r--r-- 1 geoff www 6247 Dec 30 14:11 ShellIntro.shtml -rw-r--r-- 1 geoff www 8581 Dec 30 15:13 StartUse.shtml
- cat displays a file
cp copies files
mv renames files (does not "move" them)
rm deletes files
chown changes the owner of a file (root only)
chgrp changes the group of a file (constraints)
- Any character except / is allowed. Use ''s around weird file names.
- Extensions are not meaningful to UNIX, only to applications
- Special file names
- .
- ..
- ls <directory> lists the files in the <directory>
(default is the current working directory)
- ls -F appends characters to show file type
- ls -a includes files starting with . (hidden files)
- ls -F appends characters to show file type
- mkdir makes a directory
rmdir removes an empty directory
rm -r recursively removes files and directories
- Important system directories (common places - these vary between
UNICES)
- /bin - binaries of commands
- /sbin - binaries of system admin commands
- /usr - read-only data shared between machines
- /usr/bin - shared binaries
- /usr/sbin - shared system admin commands
- /usr/local/bin - shared binaries installed locally
- /usr/local/sbin - shared system admin binaries installed locally
- /dev - files corresponding to devices
- /etc - host specific configuration files
- /home - user accounts
- /lib - libraries of objects
- /tmp - temporary stuff, deleted periodically
- /var - changing data
- /proc - information about processes
- UNIX file systems are organized as DAGs
- A file may have multiple names, "linked" from different
parts of the hierarchy.
- Hard links cannot be to directories, or across file systems
- Symbolic links are different, and provide a reference to another node in the hierarchy, for the system to follow.
- ln makes hard links
ln -s makes symbolic links
- There are three groups with access rights:
- The user who owns the file
- Members of the group associated with the file
- Other users
- There are three types of access:
- Read access
- Write access
- Execute (file) or current directory (directories) access
- chmod changes permissions
- Symbolic encoding
- The mode has the form uuugggooo to encode user, group, and other access rights
- Each letter may be one of -, r, w, x.
- Numerical Encoding
- The 9 permission bits are represented by 3 octal digits
(each digit represents 3 bits):
- 001 represents execute access for others
- 002 represents write access for others
- 004 represents read access for others
- 010 represents execute access for group
- 020 represents write access for group
- 040 represents read access for group
- 100 represents execute access for user
- 200 represents write access for user
- 400 represents read access for user
- To generate a composite mode, add up the individual modes
- Example:
rw-r--r-- is a common mode for a regular file:
the user is allowed to read and write the file, and
everyone else is allowed to read the file (no secrets ;-).
- Corresponding numerical value:
0400 User read 0200 User write 0040 Group read 0004 Other read --------------- 0644
- Corresponding numerical value:
- The 9 permission bits are represented by 3 octal digits
(each digit represents 3 bits):
- Default permissions
- The default permissions for new plain files are rw-rw-rw-, and the default permissions for new directories are rwxrwxrwx.
- Each process maintains a file mode umask that determines what access rights are not granted for newly created files and directories.
- The umask is inherited by new processes (i.e., your files will be created with rights based on the umask of your shell)
- The umask contains 9 bits, corresponding to the rwxrwxrwx access rights, and bits set in the mask are always cleared
- umask sets the umask of your shell