MPE/iX Shell and Utilities Reference Manual, Vol 2

• File limit
• MPE/iX accounting limits on disk space
File Limits
MPE/iX supports file limits on all objects created on the system to allow users to control the maximum
size a file can attain. Files created through
MPE/iX Shell and Utilities have file limits. The default file
limit for a byte stream file is two gigabytes when created through MPE/iX Shell and Utilities. A file’s
file limit cannot be manipulated through
MPE/iX Shell and Utilities.
Attempts to write data to a file that would result in that file’s size exceeding the file limit result in a
system error (see syserror(3)).
Normally, the file limit of two gigabytes should rarely, if ever, be reached; however, a user can use
MPE/iX CI commands or system intrinsics to set a file limit to a much lower value. If you open a byte
stream file with a file limit that has been set to a lower value, the chance of a write error is increased.
MPE/iX Accounting Limits on Disk Space
MPE/iX allows a system administrator to limit the amount of disk space a user may allocate.
MPE/iX disk
space limitations can only be placed on MPE/iX account directories and group directories; however, a
limit placed on an account or group directory is also imposed on all hierarchical directories and files
created at all levels beneath that account or group directory.
No such accounting limits exist for hierarchical directories and files created at all levels under the root
directory that are not under
MPE/iX account and group directories.
Attempts to write data to a file that would result in the disk allocation exceeding
MPE/iX disk space lim-
itations result in a system error (see syserror(3)).
Additional Implementation Considerations
The MPE/iX Shell and Utilities utilities 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 (//).
The current release of MPE/iX does not provide facilities that allow programs to modify their effective
user or group identities. As a result, a process’s real and effective user IDs and group IDs are always the
same.
If you use chmod to change the access permission bits of an file, the change does not affect access
through open file descriptors that are already associated with the file.
MPE/iX implements the DIR structure associated with both C streams and directory streams using a file
descriptor. You encounter one effect of this implementation when you attempt to execute a file.
Because MPE/iX uses file descriptors to implement streams, the file descriptors associated with the par-
ent’s streams remain open for the new process image and count towards the new process image’s limit
of open file descriptors; however, these file descriptors are inaccessible to the new process image.
A-8 MPE/iX Implementation Considerations