Instruction 01-linux-filesystem-and-navigation: Reading

Linux presents files through one unified directory tree beginning at the root directory, written as /. Unlike systems that expose separate drive letters, Linux normally attaches additional filesystems at directories called mount points. Common top-level locations include /etc for host configuration, /home for ordinary users' home directories, /var for changing application data, /usr for installed programs and shareable data, /run for runtime state, /tmp for temporary data, and /opt for optional or locally managed software and lab content. These are conventions described by the Filesystem Hierarchy Standard, but actual layouts can vary by distribution and deployment.

Every shell process has a current working directory. The pwd command reports it, and cd changes it. An absolute path starts with / and does not depend on the current working directory. A relative path does not start with / and is interpreted from the current working directory. The component . means the current directory, while .. means the parent directory. The shell commonly expands ~ to the current user's home directory before running a command. Because relative paths depend on context, administrators should check pwd and inspect a destination before performing a mutating operation.

A path is a sequence of directory-entry names separated by forward slashes. Directories map names to inodes. An inode stores metadata such as object type, owner, permissions, timestamps, size, and references to file data. A regular filename is therefore a directory entry pointing to an inode. A hard link creates another name for the same inode, so both names initially expose the same data and share an inode number. Removing one hard-link name does not remove the inode while another link still refers to it. A symbolic link is different: it is its own filesystem object containing a pathname. It may cross filesystem boundaries and may become dangling if its target is moved or removed.

The ls command displays directory entries, while options such as -a and -l reveal hidden names and long-format metadata. Long listings are useful, but scripts should not parse their human-oriented output when a dedicated interface such as stat or find is available. stat reports detailed metadata; file examines content or identifying characteristics; readlink displays a symbolic link's stored target; namei walks through pathname components; and find recursively selects entries according to explicit conditions. Quoting variable expansions and paths prevents whitespace or wildcard characters from being interpreted unexpectedly. Tab completion, read-only inspection, and deliberate use of absolute lab paths reduce mistakes. Hidden files are not inherently protected, file extensions do not determine Linux file type, and filesystem permissions must be evaluated together with directory permissions, ownership, process identity, mount options, and access-control systems.