An i-node doesn’t contain a file’s name. Instead, files are assigned names via entries in directories, which are tables listing filename and i-node number correspondences. These directory entries are called (hard) links. A file may have multiple links, all of which enjoy equal status. Links are created and removed using link() and unlink(). A file can be renamed using the rename() system call.
A symbolic (or soft) link is created using symlink(). Symbolic links are similar to hard links in some respects, with the differences that symbolic links can cross file-system boundaries and can refer to directories. A symbolic link is just a file containing the name of another file; this name may be retrieved using readlink(). A symbolic link is not included in the (target) i-node’s link count, and it may be left dangling if the filename to which it refers is removed. Some system calls automatically dereference (follow) symbolic links; others do not. In some cases, two versions of a system call are provided: one that dereferences symbolic links and another that does not. Examples are stat() and lstat().
Directories are created with mkdir() and removed using rmdir(). To scan the contents of a directory, we can use opendir(), readdir(), and related functions. The nftw() function allows a program to walk an entire directory tree, calling a programmer-defined function to operate on each file in the tree.
The remove() function can be used to remove a file (i.e., a link) or an empty directory.
Each process has a root directory, which determines the point from which absolute pathnames are interpreted, and a current working directory, which determines the point from which relative pathnames are interpreted. The chroot() and chdir() system calls are used to change these attributes. The getcwd() function returns a process’s current working directory.
Linux provides a set of system calls (e.g., openat()) that behave like their traditional counterparts (e.g., open()), except that relative pathnames can be interpreted with respect to the directory specified by a file descriptor supplied to the call (instead of using the process’s current working directory). This is useful for avoiding certain types of race conditions and for implementing per-thread virtual working directories.
The realpath() function resolves a pathname—dereferencing all symbolic links and resolving all references to . and .. to corresponding directories—to yield a corresponding absolute pathname. The dirname() and basename() functions can be used to parse a pathname into directory and filename components.