Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11PermissionsSetting File PermissionsSlide 14Slide 15Slide 16Slide 17Slide 18Slide 19•Let’s log on using Secure Shell.Permissions•You can set permissions for accessing your files, and you should do this.•From within a directory or subdirectory, issue a ls –l command (those are letter ls not numeral 1s)•This will list the subdirectories and files within ‘that’ subdirectory. •You can then issue a change feature (ahead) to allow / prevent certain accesses.•Typically you will use something like: (change modifications) $ chmod 755 myfile.c <return>This gives total permissions to you and read and execute permissions to ‘group’ and ‘others’ (more ahead)Setting File PermissionsFile Permissionsr Owner has readw Owner has writex Owner has executer Group has read- Group does not have writex Group has executer Others have read- Others do not have writex Others have execute1 1 1 1 0 1 1 0 175 5$ chmod 755 filenameSetting File Permissions•chmod command–To set file permissions–Syntax: $chmod UGO <file name>–Where U=user, G=group, and O=other•Setting permissions to directories–Use the execute (x) to grant accessSetting File Permissions•DO NOT CHANGE COMMANDS UNTIL YOU UNDERSTAND ALL OF THIS!!!–Practice:•$chmod 700 a_file•$chmod 640 a_directory•$chmod 604 a_file •The system you are learning is referred to as octal represented.•How else can I change user permissions with the chmod command?Setting File Permissions•Basic Unix permissions are broken up into three groups:–Owner - Can manage own files –Group -Everyone in group manages files –Others - Everyone in the world manages filesSetting File Permissions•There are three Unix file permissions:•Read (4)–You may read this file •Write (2)–You may write/delete this file •Execute (1) –You may execute this file (binary or script) –Unlike Windows, the filename's extension means nothing to the operating system. However, it is important for maintenance to follow some convention.Setting File Permissions•Common permission 1:–Owner: Read, Write –Group: Read –World: Read•Common permission 2:–Owner: Read, Write, Execute –Group: Read, Execute –World: Read, Execute •Common permission 3:–Owner: Read, Write, Execute –Group: Read, Execute –World: nothingSetting File Permissions•Each letter has a value: r=4, w=2, x=1•Add them up to determine their meaning. •rw (read/write) = (r+w) = (4+2) = 6•rwx (read/write/execute) = (r+w+x) = (4+2+1) = 7•rx (read/execute) = (r+x) = (4+1) = 5ow ner group world| | |-- --- ----- -----| || | | |-- --- -- -- -dr wxr wx rw
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