39 - Files and Directories.md

Files and Directories:

• File: A linear array of bytes with a low-level name (inode number)
• Directory: A collection of (name, inode number) pairs, mapping human-readable names to inodes
• Directory tree/hierarchy organizes all files and directories starting from the root directory

File System Interface:

• Open a file with open() system call to get a file descriptor
• Read/write files with read()/write() system calls using file descriptors
• Use lseek() to change the current offset for random access
• fsync() to force writes to persistent storage
• Create files with open() and O_CREAT flag
• Unlink/delete files with unlink() system call

Directories:

• Create directories with mkdir() system call
• Read directories with opendir(), readdir(), closedir()
• Remove empty directories with rmdir()

Links:

• Hard links create additional directory entries pointing to the same inode
• Symbolic (soft) links are special files containing a pathname
• Hard links share the same inode, symbolic links point to a pathname

File Metadata and Permissions:

• Use stat()/fstat() to get file metadata like size, inode, permissions, etc.
• Permissions control read, write, execute access for owner, group, others
• Use chmod() to change permissions

Mounting and File Systems:

• mkfs utility creates a new file system on a device
• mount attaches a file system at a mount point in the directory tree
• mount unifies multiple file systems into a single directory hierarchy