MPE/iX Shell and Utilities Reference Manual, Vol 2

• You can use the dot directory to specify the current directory without using a formal directory
name.
• You can use the dot-dot directory to specify the current directory’s parent directory without using
a formal directory name.
You can open the dot and dot-dot directories just like any other hierarchical directory. You can use file
information routines to return information about these directories.
You cannot explicitly remove these two directories from their parent directory except by removing the
parent directory.
Note: The dot and dot-dot directories are not found explicitly under the root directory or under
MPE/iX
account and group directories; however, you can use both dot and dot-dot with these directories during
path name resolution.
Additional Implementation Considerations
Two MPE/iX ACD access modes, create directory entry (CD
) and delete directory entry (DD), implement
write access to a directory. Setting or modifying write access permission to a directory using
MPE/iX
Shell and Utilities always modifies both ACD access modes. Both CD and DD access modes must
be specified in the ACD
for a MPE/iX Shell and Utilities routine to have write access to a hierarchical
directory.
MPE/iX CI
commands and system intrinsics allow you to remove either the CD or DD access mode. When
this occurs, write access permission is not visible to the user through the ls –l command; however,
if only
DD access is specified in the ACD, a user can delete directory entries but cannot create directory
entries. Likewise, if only
CD access is specified in the ACD, a user can create directory entries but can-
not delete directory entries.
The MPE/iX
Shell and Utilities routines which allow you to specify a path name return a system error
(see syserror(3)) if you attempt to specify a path name beginning with two slash characters (//).
If you use chmod to change the access permission bits of a file or directory, the change does not affect
access through open file descriptors already associated with the file or directory.
Because MPE/iX uses file descriptors to implement directory streams, the file descriptors associated with
the parent’s directory streams remain open for the new process image and count towards the new pro-
cess image’s limit of open file descriptors. These file descriptors, however, are inaccessible to the new
process image.
If you add an entry to or remove an entry from a directory, subsequent queries of the directory accu-
rately reflect its current state.
Each directory has a maximum link count of 1. MPE/iX considers a directory removed if its link count is
zero. MPE/iX Shell and Utilities routines that are accessing a directory file when its link count becomes
zero can continue to access the directory; however, upon closing the directory, the routine cannot again
open the directory.
MPE/iX Implementation Considerations A-13