chmod man page on Oracle

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CHMOD(3P)		   POSIX Programmer's Manual		     CHMOD(3P)

       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

       chmod - change mode of a file

       #include <sys/stat.h>

       int chmod(const char *path, mode_t mode);

       The chmod() function shall change S_ISUID, S_ISGID,  S_ISVTX,  and  the
       file  permission	 bits  of the file named by the pathname pointed to by
       the path argument to the corresponding bits in the mode	argument.  The
       application  shall  ensure  that	 the  effective user ID of the process
       matches the owner of the file or the process has appropriate privileges
       in order to do this.

       S_ISUID, S_ISGID,  S_ISVTX,  and the file permission bits are described
       in <sys/stat.h>.

       If the calling process does not have appropriate privileges, and if the
       group  ID  of  the file does not match the effective group ID or one of
       the supplementary group IDs and if the file  is	a  regular  file,  bit
       S_ISGID (set-group-ID on execution) in the file's mode shall be cleared
       upon successful return from chmod().

       Additional implementation-defined restrictions may  cause  the  S_ISUID
       and S_ISGID bits in mode to be ignored.

       The  effect on file descriptors for files open at the time of a call to
       chmod() is implementation-defined.

       Upon successful completion, chmod() shall mark for update the  st_ctime
       field of the file.

       Upon successful completion, 0 shall be returned; otherwise, -1 shall be
       returned and errno set to indicate the error. If	 -1  is	 returned,  no
       change to the file mode occurs.

       The chmod() function shall fail if:

       EACCES Search permission is denied on a component of the path prefix.

       ELOOP  A loop exists in symbolic links encountered during resolution of
	      the path argument.

	      The length of the path argument exceeds {PATH_MAX} or a pathname
	      component is longer than {NAME_MAX}.

	      A component of the path prefix is not a directory.

       ENOENT A component of path does not name an existing file or path is an
	      empty string.

       EPERM  The effective user ID does not match the owner of the  file  and
	      the process does not have appropriate privileges.

       EROFS  The named file resides on a read-only file system.

       The chmod() function may fail if:

       EINTR  A signal was caught during execution of the function.

       EINVAL The value of the mode argument is invalid.

       ELOOP  More  than  {SYMLOOP_MAX} symbolic links were encountered during
	      resolution of the path argument.

	      As a result of encountering a symbolic link in resolution of the
	      path  argument,  the  length of the substituted pathname strings
	      exceeded {PATH_MAX}.

       The following sections are informative.

   Setting Read Permissions for User, Group, and Others
       The following example sets read permissions for the owner,  group,  and

	      #include <sys/stat.h>

	      const char *path;
	      chmod(path, S_IRUSR|S_IRGRP|S_IROTH);

   Setting Read, Write, and Execute Permissions for the Owner Only
       The following example sets read, write, and execute permissions for the
       owner, and no permissions for group and others.

	      #include <sys/stat.h>

	      const char *path;
	      chmod(path, S_IRWXU);

   Setting Different Permissions for Owner, Group, and Other
       The following example sets owner permissions for	 CHANGEFILE  to	 read,
       write,  and  execute,  group permissions to read and execute, and other
       permissions to read.

	      #include <sys/stat.h>

	      #define CHANGEFILE "/etc/myfile"

   Setting and Checking File Permissions
       The following example sets the file permission bits for	a  file	 named
       /home/cnd/mod1,	then  calls  the stat() function to verify the permis‐

	      #include <sys/types.h>
	      #include <sys/stat.h>

	      int status;
	      struct stat buffer
	      chmod("home/cnd/mod1", S_IRWXU|S_IRWXG|S_IROTH|S_IWOTH);
	      status = stat("home/cnd/mod1", &buffer;);

       In order to ensure that the S_ISUID and S_ISGID bits are set, an appli‐
       cation  requiring  this should use stat() after a successful chmod() to
       verify this.

       Any file descriptors currently open by any process on  the  file	 could
       possibly	 become	 invalid if the mode of the file is changed to a value
       which would deny access to that process. One situation where this could
       occur  is on a stateless file system. This behavior will not occur in a
       conforming environment.

       This volume of IEEE Std 1003.1-2001 specifies that the S_ISGID  bit  is
       cleared	by chmod() on a regular file under certain conditions. This is
       specified on the assumption that regular files may be executed, and the
       system  should prevent users from making executable setgid() files per‐
       form with privileges that the caller does not have. On  implementations
       that  support  execution of other file types, the S_ISGID bit should be
       cleared for those file types under the same circumstances.

       Implementations that use the S_ISUID bit to indicate some  other	 func‐
       tion  (for  example,  mandatory record locking) on non-executable files
       need not clear this bit on writing. They should clear the bit for  exe‐
       cutable	files  and any other cases where the bit grants special powers
       to processes that change the file contents.  Similar comments apply  to
       the S_ISGID bit.


       chown(), mkdir(), mkfifo(), open(), stat(), statvfs(), the Base Defini‐
       tions volume of IEEE Std 1003.1-2001, <sys/stat.h>, <sys/types.h>

       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the	referee document. The original Standard can be obtained online
       at .

IEEE/The Open Group		     2003			     CHMOD(3P)

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