bsd/man/man2/chmod.2

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  34 .\"     @(#)chmod.2     8.1 (Berkeley) 6/4/93
  35 .\"
  36 .Dd June 4, 1993
  37 .Dt CHMOD 2
  38 .Os BSD 4
  39 .Sh NAME
  40 .Nm chmod ,
  41 .Nm fchmod
  42 .Nd change mode of file
  43 .Sh SYNOPSIS
  44 .Fd #include <sys/types.h>
  45 .Fd #include <sys/stat.h>
  46 .Ft int
  47 .Fn chmod "const char *path" "mode_t mode"
  48 .Ft int
  49 .Fn fchmod "int fd" "mode_t mode"
  50 .Sh DESCRIPTION
  51 The function
  52 .Fn chmod
  53 sets the file permission bits
  54 of the file
  55 specified by the pathname
  56 .Fa path
  57 to
  58 .Fa mode .
  59 .Fn Fchmod
  60 sets the permission bits of the specified
  61 file descriptor
  62 .Fa fd .
  63 .Fn Chmod
  64 verifies that the process owner (user) either owns
  65 the file specified by
  66 .Fa path
  67 (or
  68 .Fa fd ) ,
  69 or
  70 is the super-user.
  71 A mode is created from
  72 .Em or'd
  73 permission bit masks
  74 defined in
  75 .Aq Pa sys/stat.h :
  76 .Bd -literal -offset indent -compact
  77 #define S_IRWXU 0000700    /* RWX mask for owner */
  78 #define S_IRUSR 0000400    /* R for owner */
  79 #define S_IWUSR 0000200    /* W for owner */
  80 #define S_IXUSR 0000100    /* X for owner */
  81
  82 #define S_IRWXG 0000070    /* RWX mask for group */
  83 #define S_IRGRP 0000040    /* R for group */
  84 #define S_IWGRP 0000020    /* W for group */
  85 #define S_IXGRP 0000010    /* X for group */
  86
  87 #define S_IRWXO 0000007    /* RWX mask for other */
  88 #define S_IROTH 0000004    /* R for other */
  89 #define S_IWOTH 0000002    /* W for other */
  90 #define S_IXOTH 0000001    /* X for other */
  91
  92 #define S_ISUID 0004000    /* set user id on execution */
  93 #define S_ISGID 0002000    /* set group id on execution */
  94 #define S_ISVTX 0001000    /* save swapped text even after use */
  95 .Ed
  96 .Pp
  97 The
  98 .Dv ISVTX
  99 (the
 100 .Em sticky bit )
 101 indicates to the system which executable files are shareable (the
 102 default) and the system maintains the program text of the files
 103 in the swap area. The sticky bit may only be set by the super user
 104 on shareable executable files.
 105 .Pp
 106 If mode
 107 .Dv ISVTX
 108 (the `sticky bit') is set on a directory,
 109 an unprivileged user may not delete or rename
 110 files of other users in that directory. The sticky bit may be
 111 set by any user on a directory which the user owns or has appropriate
 112 permissions.
 113 For more details of the properties of the sticky bit, see
 114 .Xr sticky 8 .
 115 .Pp
 116 Writing or changing the owner of a file
 117 turns off the set-user-id and set-group-id bits
 118 unless the user is the super-user.
 119 This makes the system somewhat more secure
 120 by protecting set-user-id (set-group-id) files
 121 from remaining set-user-id (set-group-id) if they are modified,
 122 at the expense of a degree of compatibility.
 123 .Sh RETURN VALUES
 124 Upon successful completion, a value of 0 is returned.
 125 Otherwise, a value of -1 is returned and
 126 .Va errno
 127 is set to indicate the error.
 128 .Sh ERRORS
 129 .Fn Chmod
 130 will fail and the file mode will be unchanged if:
 131 .Bl -tag -width Er
 132 .It Bq Er ENOTDIR
 133 A component of the path prefix is not a directory.
 134 .It Bq Er ENAMETOOLONG
 135 A component of a pathname exceeded
 136 .Dv {NAME_MAX}
 137 characters, or an entire path name exceeded
 138 .Dv {PATH_MAX}
 139 characters.
 140 .It Bq Er ENOENT
 141 The named file does not exist.
 142 .It Bq Er EACCES
 143 Search permission is denied for a component of the path prefix.
 144 .It Bq Er ELOOP
 145 Too many symbolic links were encountered in translating the pathname.
 146 .It Bq Er EPERM
 147 The effective user ID does not match the owner of the file and
 148 the effective user ID is not the super-user.
 149 .It Bq Er EROFS
 150 The named file resides on a read-only file system.
 151 .It Bq Er EFAULT
 152 .Fa Path
 153 points outside the process's allocated address space.
 154 .It Bq Er EIO
 155 An I/O error occurred while reading from or writing to the file system.
 156 .El
 157 .Pp
 158 .Fn Fchmod
 159 will fail if:
 160 .Bl -tag -width Er
 161 .It Bq Er EBADF
 162 The descriptor is not valid.
 163 .It Bq Er EINVAL
 164 .Fa fd
 165 refers to a socket, not to a file.
 166 .It Bq Er EROFS
 167 The file resides on a read-only file system.
 168 .It Bq Er EIO
 169 An I/O error occurred while reading from or writing to the file system.
 170 .El
 171 .Sh SEE ALSO
 172 .Xr chmod 1 ,
 173 .Xr open 2 ,
 174 .Xr chown 2 ,
 175 .Xr stat 2 ,
 176 .Xr sticky 8
 177 .Sh STANDARDS
 178 The
 179 .Fn chmod
 180 function is expected to conform to
 181 .St -p1003.1-88 .
 182 .Sh HISTORY
 183 The
 184 .Fn fchmod
 185 function call
 186 appeared in
 187 .Bx 4.2 .