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Top Forums UNIX for Dummies Questions & Answers Permission Question Post 302269218 by Tiger75 on Wednesday 17th of December 2008 05:56:33 AM

12-17-2008

Registered User

s stands for setting the User ID/Group ID.
t stands for setting the Sticky bit

SUID or setuid: change user ID on execution. If setuid bit is set, when the file will be executed by a user, the process will have the same rights as the owner of the file being executed.
SGID or setgid: change group ID on execution. Same as above, but inherits rights of the group of the owner of the file. For directories it also may mean that when a new file is created in the directory it will inherit the group of the directory (and not of the user who created the file).
Sticky bit. It was used to trigger process to "stick" in memory after it is finished, now this usage is obsolete. Currently its use is system dependant and it is mostly used to suppress deletion of the files that belong to other users in the folder where you have "write" access to.

The most common use of the sticky bit today is on directories, where, when set, items inside the directory can only be renamed or deleted by the item's owner, the directory's owner, or the superuser. Generally this is set on the /tmp directory to prevent ordinary users from deleting or moving other users' files.
The sticky bit can only be set by superuser root. Using the chmod command, it can be set using its octal mode 1000 or by its symbol t (s is already used by the setuid bit).
SUID stands for "Set User-ID". If the suid bit is enable on an executable, then whenever that program is run the process will take on the privilege of whoever the file owner is. For example if I have a suid binary which is owned by "root" and I execute it as my normal (non-root) user name, it will execute with all the permissions of root.

SUIDIf set, then replaces "x" in the owner permissions to "s", if owner has execute permissions, or to "S" otherwise. Examples:
-rws------ both owner execute and SUID are set
-r-S------ SUID is set, but owner execute is not setSGIDIf set, then replaces "x" in the group permissions to "s", if group has execute permissions, or to "S" otherwise. Examples:
-rwxrws--- both group execute and SGID are set
-rwxr-S--- SGID is set, but group execute is not setStickyIf set, then replaces "x" in the others permissions to "t", if others have execute permissions, or to "T" otherwise. Examples:
-rwxrwxrwt both others execute and sticky bit are set
-rwxrwxr-T sticky bit is set, but others execute is not set

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LEARN ABOUT CENTOS

stat.h

stat.h(3HEAD)                                                         Headers                                                        stat.h(3HEAD)

NAME

       stat.h, stat - data returned by stat system call

SYNOPSIS

       #include <sys/types.h>

       #include <sys/stat.h>

DESCRIPTION

       The system calls stat, lstat and fstat return data in a stat structure, which is defined in <stat.h>.

       The constants used in the st_mode field are also defined in this file:

       #define    S_IFMT           /* type of file */
       #define    S_IAMB           /* access mode bits */
       #define    S_IFIFO          /* fifo */
       #define    S_IFCHR          /* character special */
       #define    S_IFDIR          /* directory */
       #define    S_IFNAM          /* XENIX special named file */
       #define    S_INSEM          /*  XENIX  semaphore  subtype  of
                                   IFNAM */
       #define    S_INSHD          /* XENIX shared data  subtype  of
                                   IFNAM */
       #define    S_IFBLK          /* block special */
       #define    S_IFREG          /* regular */
       #define    S_IFLNK          /* symbolic link */
       #define    S_IFSOCK         /* socket */
       #define    S_IFDOOR         /* door */
       #define    S_ISUID          /* set user id on execution */
       #define    S_ISGID          /* set group id on execution */
       #define    S_ISVTX          /*  save  swapped text even after
                                   use */
       #define    S_IREAD          /* read permission, owner */
       #define    S_IWRITE         /* write permission, owner */
       #define    S_IEXEC          /*   execute/search   permission,
                                   owner */
       #define    S_ENFMT          /*   record  locking  enforcement
                                   flag */
       #define    S_IRWXU          /* read, write, execute: owner */
       #define    S_IRUSR          /* read permission: owner */
       #define    S_IWUSR          /* write permission: owner */
       #define    S_IXUSR          /* execute permission: owner */
       #define    S_IRWXG          /* read, write, execute: group */
       #define    S_IRGRP          /* read permission: group */
       #define    S_IWGRP          /* write permission: group */
       #define    S_IXGRP          /* execute permission: group */
       #define    S_IRWXO          /* read, write, execute: other */
       #define    S_IROTH          /* read permission: other */
       #define    S_IWOTH          /* write permission: other */
       #define    S_IXOTH          /* execute permission: other */

       The following macros are for POSIX conformance (see standards(5)):

       #define    S_ISBLK(mode)    block special file
       #define    S_ISCHR(mode)    character special file
       #define    S_ISDIR(mode)    directory file
       #define    S_ISFIFO(mode)   pipe or fifo file
       #define    S_ISREG(mode)    regular file

       #define    S_ISSOCK(mode)   socket file

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Interface Stability          |Standard                     |
       +-----------------------------+-----------------------------+

SEE ALSO

       stat(2), types.h(3HEAD), attributes(5), standards(5)

SunOS 5.10                                                          30 Aug 2002                                                      stat.h(3HEAD)

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