fchmod(2) - osol9

1chmod(2)                         System Calls                         chmod(2)
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NAME

6       chmod, fchmod - change access permission mode of file
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SYNOPSIS

9       #include <sys/types.h>
10       #include <sys/stat.h>
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12       int chmod(const char *path, mode_t mode);
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14
15       int fchmod(int fildes, mode_t mode);
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DESCRIPTION

19       The chmod() and fchmod() functions set the access permission portion of
20       the mode of the file whose name is given by path or referenced  by  the
21       open  file  descriptor  fildes  to  the  bit pattern contained in mode.
22       Access permission bits are interpreted as follows:
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27       S_ISUID      04000     Set user ID on execution.
28       S_ISGID      020#0     Set group ID on execution if # is 7,  5,
29                              3,  or  1.  Enable mandatory file/record
30                              locking if # is 6, 4, 2, or 0.
31       S_ISVTX      01000     Sticky bit.
32       S_IRWXU      00700     Read, write, execute by owner.
33       S_IRUSR      00400     Read by owner.
34       S_IWUSR      00200     Write by owner.
35       S_IXUSR      00100     Execute  (search  if  a  directory)   by
36                              owner.
37       S_IRWXG      00070     Read, write, execute by group.
38       S_IRGRP      00040     Read by group.
39       S_IWGRP      00020     Write by group.
40       S_IXGRP      00010     Execute by group.
41       S_IRWXO      00007     Read, write, execute (search) by others.
42       S_IROTH      00004     Read by others.
43       S_IWOTH      00002     Write by others.
44       S_IXOTH      00001     Execute by others.
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48       Modes are constructed by the bitwise OR operation of the access permis‐
49       sion bits.
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52       The effective user ID of the process must match the owner of  the  file
53       or  the  process must have the appropriate privilege to change the mode
54       of a file.
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57       If the process is not a privileged process and the file is not a direc‐
58       tory, mode bit 01000 (save text image on execution) is cleared.
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61       If  neither  the process is privileged nor the file's group is a member
62       of the process's  supplementary group list, and the effective group  ID
63       of  the process does not match the group ID of the file, mode bit 02000
64       (set group ID on execution) is cleared.
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67       If a directory is writable and has S_ISVTX (the sticky bit) set,  files
68       within  that directory can be removed or renamed only if one or more of
69       the following is true (see unlink(2) and rename(2)):
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71           o      the user owns the file
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73           o      the user owns the directory
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75           o      the file is writable by the user
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77           o      the user is a privileged user
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80       If a regular file is not executable and has S_ISVTX set,  the  file  is
81       assumed  to  be a swap file. In this case, the system's page cache will
82       not be used to hold the file's data. If the S_ISVTX bit is set  on  any
83       other file, the results are unspecified.
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86       If  a  directory  has  the  set  group ID bit set, a given file created
87       within that directory will have  the same group ID  as  the  directory.
88       Otherwise,  the newly created file's group ID will be set to the effec‐
89       tive group ID of the creating process.
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92       If the mode bit 02000 (set group ID on execution) is set and  the  mode
93       bit   00010  (execute  or  search  by  group)  is  not  set,  mandatory
94       file/record locking will exist on a regular  file,  possibly  affecting
95       future calls to open(2), creat(2), read(2), and write(2) on this file.
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98       If  fildes references a shared memory object, fchmod() need only affect
99       the S_IRUSR, S_IRGRP,  S_IROTH,  S_IWUSR,  S_IWGRP,  S_IWOTH,  S_IXUSR,
100       S_IXGRP, and S_IXOTH file permission bits.
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103       If  fildes  refers to a socket, fchmod() does not fail but no action is
104       taken.
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107       If fildes refers to a stream that is attached to an object in the  file
108       system  name  space  with  fattach(3C),  the  fchmod() call performs no
109       action and returns successfully.
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112       Upon successful completion, chmod() and fchmod() mark  for  update  the
113       st_ctime field of the file.
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RETURN VALUES

116       Upon  successful  completion, 0 is returned. Otherwise, −1 is returned,
117       the file mode is unchanged, and errno is set to indicate the error.
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ERRORS

120       The chmod() and fchmod() functions will fail if:
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122       EIO      An I/O error occurred while reading from  or  writing  to  the
123                file system.
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126       EPERM    The effective user ID does not match the owner of the file and
127                the process does not have appropriate privilege.
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129                The {PRIV_FILE_OWNER} privilege overrides constraints on  own‐
130                ership when changing permissions on a file.
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132                The  {PRIV_FILE_SETID} privilege overrides constraints on own‐
133                ership when adding the setuid or setgid bits to an  executable
134                file  or  a  directory.   When adding the setuid bit to a root
135                owned executable, additional restrictions  apply.  See  privi‐
136                leges(5).
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139
140       The chmod() function will fail if:
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142       EACCES          Search  permission is denied on a component of the path
143                       prefix of path. The privilege  {FILE_DAC_SEARCH}  over‐
144                       rides file permissions restrictions in that case.
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147       EFAULT          The path argument points to an illegal address.
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150       ELOOP           A  loop exists in symbolic links encountered during the
151                       resolution of the path argument.
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154       ENAMETOOLONG    The length of the path argument  exceeds  PATH_MAX,  or
155                       the  length  of a path component exceeds NAME_MAX while
156                       _POSIX_NO_TRUNC is in effect.
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159       ENOENT          Either a component of  the  path  prefix  or  the  file
160                       referred  to  by path does not exist or is a null path‐
161                       name.
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164       ENOLINK         The fildes argument points to a remote machine and  the
165                       link to that machine is no longer active.
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168       ENOTDIR         A component of the prefix of path is not a directory.
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171       EROFS           The  file  referred  to  by path resides on a read-only
172                       file system.
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175
176       The fchmod() function will fail if:
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178       EBADF      The fildes argument is not an open file descriptor
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181       ENOLINK    The path argument points to a remote machine and the link to
182                  that machine is no longer active.
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185       EROFS      The  file  referred to by fildes resides on a read-only file
186                  system.
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190       The chmod() and fchmod() functions may fail if:
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192       EINTR     A signal was caught during execution of the function.
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195       EINVAL    The value of the mode argument is invalid.
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199       The chmod() function may fail if:
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201       ELOOP           More than {SYMLOOP_MAX} symbolic links were encountered
202                       during the resolution of the path argument.
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205       ENAMETOOLONG    As  a result of encountering a symbolic link in resolu‐
206                       tion of thepath argument, the length of the substituted
207                       pathname strings exceeds {PATH_MAX}.
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210
211       The fchmod() function may fail if:
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213       EINVAL    The fildes argument refers to a pipe and the system disallows
214                 execution of this function on a pipe.
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216

EXAMPLES

218       Example 1 Set Read Permissions for User, Group, and Others
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220
221       The following example sets read permissions for the owner,  group,  and
222       others.
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224
225         #include <sys/stat.h>
226         const char *path;
227         ...
228         chmod(path, S_IRUSR|S_IRGRP|S_IROTH);
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230
231       Example 2 Set Read, Write, and Execute Permissions for the Owner Only
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234       The following example sets read, write, and execute permissions for the
235       owner, and no permissions for group and others.
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237
238         #include <sys/stat.h>
239         const char *path;
240         ...
241         chmod(path, S_IRWXU);
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243
244       Example 3 Set Different Permissions for Owner, Group, and Other
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247       The following example sets owner permissions for  CHANGEFILE  to  read,
248       write,  and  execute,  group permissions to read and execute, and other
249       permissions to read.
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251
252         #include <sys/stat.h>
253         #define CHANGEFILE "/etc/myfile"
254         ...
255         chmod(CHANGEFILE, S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH);
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257
258       Example 4 Set and Checking File Permissions
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260
261       The following example sets the file permission bits for  a  file  named
262       /home/cnd/mod1,  then  calls the stat(2) function to verify the permis‐
263       sions.
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265
266         #include <sys/types.h>
267         #include <sys/stat.h>
268         int status;
269         struct stat buffer
270         ...
271         chmod("home/cnd/mod1", S_IRWXU|S_IRWXG|S_IROTH|S_IWOTH);
272         status = stat("home/cnd/mod1", &buffer;);
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USAGE

276       If chmod() or fchmod() is used to change the file group  owner  permis‐
277       sions  on a file with non-trivial ACL entries, only the ACL mask is set
278       to the new permissions and the  group  owner  permission  bits  in  the
279       file's  mode  field (defined in mknod(2)) are unchanged.  A non-trivial
280       ACL entry is one whose meaning cannot be represented in the file's mode
281       field  alone.  The new ACL mask permissions  might change the effective
282       permissions for additional users and groups that have  ACL  entries  on
283       the file.
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ATTRIBUTES

286       See attributes(5) for descriptions of the following attributes:
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291       ┌─────────────────────────────┬─────────────────────────────┐
292       │      ATTRIBUTE TYPE         │      ATTRIBUTE VALUE        │
293       ├─────────────────────────────┼─────────────────────────────┤
294       │Interface Stability          │Standard                     │
295       ├─────────────────────────────┼─────────────────────────────┤
296       │MT-Level                     │Async-Signal-Safe            │
297       └─────────────────────────────┴─────────────────────────────┘
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