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How UNIX admin set up this? how files of 744 of other owner can be removed by another owner?
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chmod(1) General Commands Manual chmod(1) Name chmod - change file mode Syntax chmod [ -fR ] mode file... Description Permissions on files are set according to mode and file parameters. For file, you can specify either a full or partial path. You can specify multiple files, separated by spaces. For mode, you specify one of two variants: absolute mode or symbolic mode. Absolute Mode For mode in absolute form, you specify an octal number constructed from the sum of one or more of the following values: 4000 set user ID on execution (applies to executable files only) 2000 set group ID on execution (applies to executable files only) 1000 set sticky bit (see for more information) 0400 read by owner 0200 write by owner 0100 execute, or search if file is a directory, by owner 0040 read by group 0020 write by group 0010 execute, or search if file is a directory, by group 0004 read by others 0002 write by others 0001 execute, or search if file is a directory, by others For example, the absolute mode value that provides read, write, and execute permission to owner, read and execute permission to group, and read and execute permission to others is 755 (400+200+100+40+10+4+1). The absolute mode value that provides read, write, and execute per- mission to owner and no permission to group or others is 700 (400+200+100). Symbolic Mode To specify mode in symbolic form, use the following format: [who] op permission [op permission] ... Spaces are included in the preceding format so that you can read the arguments; however, as will be shown in examples that follow, you do not enter spaces between mode arguments. Specify who using the letters u (for owner), g (for group) and o (for others) either alone or in combination. You can also specify the letter a (for all), which is is equivalent to the letter combination ugo. If you omit the who parameter, a is assumed. For more informa- tion, see For the op parameter, specify the plus sign (+) to add permission to the file's mode, the minus sign (-) to remove permission from the file's mode, or the equal sign (=) to assign permission absolutely (denying or revoking any permission not explicitly specified following the equal sign). The first command in the following example provides group with execute permission for in addition to any other permis- sions group currently has for The second command limits the permission that group has for to execute alone: chmod g+x filea chmod g=x fileb For the permission parameter, specify any combination of the letters r (read), w (write), x (execute), s (set owner or group id), and t (save text - sticky). Alternatively, you can specify the letter u, g, or o to set permission for the who parameter to be the same as the permission currently granted to the user category indicated by the letter. In the following example, the group (g) is given the same per- missions on as currently granted to owner (u): chmod g=u filea You can revoke all permissions by specifying the who argument followed by =, and omitting the permission argument. For example, the fol- lowing command removes all permissions from others for chmod o= fileb When specifying more than one symbolic mode for file, separate the modes with commas. The mode changes are applied in the sequence speci- fied. In the following example, write permission is added to the permissions already granted to the owner of and group is then granted the same permissions on as granted the owner: chmod u+w,g=u filea Options -f Inhibits display of errors that are returned if fails to change the mode on a file. -R Causes to recursively descend any directories subordinate to file and to set the specified mode for each file encountered. However, when symbolic links are encountered, does not change the mode of the link file and does not traverse the path associated with the link. Note that the option is useful only when file identifies a directory that is not empty. Restrictions The permission letter s is used only with who letter u or g. Only the owner of a file or someone logged on as superuser may change the mode of that file. Examples Using absolute mode, provide read, write, and search permission to the owner, and read and search permission to others for a directory named chmod 755 ~harris/public Using absolute mode, set the UID for execution to be the UID of of the file owner rather than the UID of the user running the program as follows: chmod 4000 progrmb Using symbolic mode, perform the same operation as described for the preceding example: chmod u=s progrmb Using symbolic mode, deny write permission to others for the file chmod o-w ourspec Using symbolic mode, give execute permission on file to all user categories: chmod +x myprog Using symbolic mode, give write permission to all group members, deny write permission to others, and give search permission to owner on chmod g+w,o-r,u+x docdir Using symbolic mode, give read and execute permissions to others for a directory named and then recursively descend the paths subordinate to adding the same permissions for others on all files and directories included in the subordinate paths: chmod -R o+rx programs In the preceding example, if were the name of a file rather than a directory, would change the mode only of the file. See Also ls(1), chmod(2), stat(2), umask(2), chown(8) chmod(1)
