Function

fchattr invokes the fchattr callable service to modify the attributes that are associated with a file represented by a file descriptor. You can change the mode, owner, access time, modification time, change time, reference time, audit flags, general attribute flags, and file size.

Parameters

fd

The file descriptor for the file.

attribute_list

A list of attributes to be set and their values. The attributes are expressed either as numeric values (see REXX predefined variables), or as the predefined variables beginning with ST_ followed by arguments for that attribute. The attributes that may be changed and their parameters are:

Variable	Description
ST_CCSID	Coded character set ID; first 4 characters are the file tag.
ST_MODE	1 argument: permission bits as 3 octal digits.
ST_UID	2 arguments: UID and GID numbers.
ST_SIZE	1 argument: new file size.
ST_ATIME	1 argument for access time: new time or -1 for TOD.
ST_MTIME	1 argument for modification time: new time or -1 for TOD.
ST_CTIME	1 argument for change time: new time or -1 for TOD.
ST_SETUID	No arguments.
ST_SETGID	No arguments.
ST_AAUDIT	1 argument: new auditor audit value.
ST_UAUDIT	1 argument: new user audit value.
ST_STICKY	No arguments.
ST_GENVALUE	2 arguments: names of two variables. The first variable contains the general attribute mask and the second contains the general attribute value.
ST_RTIME	1 argument for reference time: new time or -1 for TOD.
ST_FILEFMT	Format of the file. To specify the format, you can specify a numeric value (see REXX predefined variables) or one of the following predefined variables used to derive the appropriate numeric value: S_FFBINARY Binary data S_FFCR Text data delimited by a carriage return character S_FFCRLF Text data delimited by carriage return and line feed characters S_FFCRNL A text file with lines delimited by carriage-return and newline characters. S_FFLF Text data delimited by a line feed character S_FFLFCR Text data delimited by a line feed and carriage return characters S_FFNA Text data with the file format not specified S_FFNL Text data delimited by a newline character S_FFRECORD File data consisting of records with prefixes. The record prefix contains the length of the record that follows.

Usage notes

1. Some of the attributes changed by the fchattr service can also be changed by other services.
2. When changing the mode:
   • The effective UID of the calling process must match the file's owner UID, or the caller must have appropriate privileges.
   • Setting the set-group-ID-on-execution permission (in mode) means that when this file is run (through the exec service), the effective GID of the caller is set to the file's owner GID, so that the caller seems to be running under the GID of the file, rather than that of the actual invoker.
     The set-group-ID-on-execution permission is set to zero if both of the following are true:

     • The caller does not have appropriate privileges.
     • The GID of the file's owner does not match the effective GID, or one of the supplementary GIDs, of the caller.
   • Setting the set-user-ID-on-execution permission (in mode) means that when this file is run, the process's effective UID is set to the file's owner UID, so that the process seems to be running under the UID of the file's owner, rather than that of the actual invoker.
3. When changing the owner:
   • For changing the owner UID of a file, the caller must have appropriate privileges.
   • For changing the owner GID of a file, the caller must have appropriate privileges, or meet all of these conditions:
     • The effective UID of the caller matches the file's owner UID.
     • The owner UID value specified in the change request matches the file's owner UID.
     • The GID value specified in the change request is the effective GID, or one of the supplementary GIDs, of the caller.
   • When the owner is changed, the set-user-ID-on-execution and set-group-ID-on-execution permissions of the file mode are automatically turned off.
   • When the owner is changed, both UID and GID must be specified as they are to be set. If you want to change only one of these values, you need to set the other to its present value for it to remain unchanged.
4. For general attribute bits to be changed, the calling process must have write permission for the file.
5. When changing the file size:
   • The change is made beginning from the first byte of the file. If the file was previously larger than the new size, the data from file_size to the original end of the file is removed. If the file was previously shorter than file_size, bytes between the old and new lengths are read as zeros. The file offset is not changed.
   • If file_size is greater than the current file size limit for the process, the request fails with EFBIG and the SIGXFSZ signal is generated for the process.
   • Successful change clears the set-user-ID, set-group-ID, and save-text (sticky bit) attributes of the file unless the caller is a superuser.
6. When changing times:
   • For the access time or the modification time to be set explicitly (using either st_atime or st_mtime with the new time), the effective ID must match that of the file's owner, or the process must have appropriate privileges.
   • For the access time or modification time to be set to the current time (using either st_atime or st_mtime with -1), the effective ID must match that of the file's owner, the calling process must have write permission for the file, or the process must have appropriate privileges.
   • For the change time or the reference time to be set explicitly (using either st_ctime or st_rtime with the new time) the effective ID must match that of the file's owner, or the process must have appropriate privileges.
   • For the change time or reference time to be set to the current time (using either st_ctime or st_rtime with -1), the calling process must have write permission for the file.
   • When any attribute field is changed successfully, the file's change time is also updated.
7. For auditor audit flags to be changed, the user must have auditor authority. The user with auditor authority can set the auditor options for any file, even those to which they do not have path access or authority to use for other purposes.

   Auditor authority is established by issuing the TSO/E command ALTUSER AUDITOR.

8. For the user audit flags to be changed, the user must have appropriate privileges or be the owner of the file.
9. The tagging of /dev/null, /dev/zero, /dev/random, and /dev/urandom is ignored.