Chapter 6. Controlling Access to Files with Linux File System Permissions.
Linux file system permissions
Access to files by users are controlled by file permissions.
r (read) = 4 w (write) = 2 x (exec) = 1
Viewing file/directory per missions and ownership
# ls -l
Changing file/directory permissions # chmod whowhatwhich file|directory who is u, g, o, a (for user, group, other, all)what is +, -, = (for add, remove, set exactly)which is r, w, x (for read, write, executable)# chmod ### file|directory # is sum of r = 4, w = 2, and x = 1
Changing file/directory user or group ownership
# chown owner:group file|directory chown can be used with the -R option to recursively change the ownership of an entire directory tree.
Special permissions
Default file permissions
# umask 0002
後面三個數字與一般權限有關， 第一個數字表示特殊權限(參考上面第5點說明)。 0 0 0 2 special + user + group + other 此 umask 表示：使用者新增檔案或目錄時，針對 other 的 權限要扣除 2，也就是不開放寫入權限。
