Detailed Explanation of Linux File Permissions: Must-Know Knowledge for Beginners
Linux file permissions are the core of system security, controlling user access methods to prevent misoperations or data breaches. Files are associated with three types of users: the owner (highest authority), the associated group (shared within the group), and others. Permissions are divided into three categories: read (r=4), write (w=2), and execute (x=1). Permissions can be represented in two forms: symbolic (e.g., `rwxrwxrwx`, where the first character indicates the file type, and the next three groups represent permissions for the three user categories) and numeric (octal, where the sum of permissions for the three user categories gives the value, e.g., `755`). Proficiency in mutual conversion between these forms is required. File and directory permissions differ: for files, `r` = view, `w` = modify/delete, `x` = execute; for directories, `r` = list contents, `w` = create/delete, `x` = enter. To modify permissions, use `chmod` (in symbolic or numeric form with `-R` for recursive directory changes) and `chown` (to change owner/group). Special permissions (SUID/SGID/SBIT) are used for specific scenarios. Mastery of symbolic-numeric conversion, `chmod` usage, and the differences between file and directory permissions enables proficiency through practice.
Read MoreEssential for Beginners: A Detailed Explanation of Linux User Permission Management
Linux permission management is the core of security and collaboration in multi-user systems, aiming to protect system security (preventing misoperations and malicious behaviors) and enable division of labor and collaboration (different users obtaining permissions as needed). Core concepts include three types of users (ordinary users, system users, root), user groups (for unified permission management), and file/directory permissions divided into three categories: owner, group, and others. Each category corresponds to three operations: read (r), write (w), and execute (x) (e.g., a directory requires x permission to be entered). To view permissions, use `ls -l`. To modify permissions, use `chmod` (numerical method: r=4, w=2, x=1; e.g., 754 represents rwxr-xr--; symbolic method: `+/-/=` to add/remove/set permissions, e.g., `u+x` adds execute permission to the owner). Ownership or group can be changed via `chown`/`chgrp`. Common issues to note: Files cannot be modified mostly due to permission or ownership problems; directories cannot be accessed without x permission; ordinary users use `sudo` to escalate privileges. Security recommendations: Minimize root usage, do not grant write permissions to others, and regularly check permissions. Master `ls -l`, `chmod`, and `chown`.
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