As with normal arguments, all return codes and values from functions are of type integer unless otherwise noted. An error number is also made available in the external variable errno, which is not cleared on successful calls. Thus errno should be tested only after an error has occurred.
The following is a complete list of the errors and their names as given in <sys/errno.h>.
Each user is also a member of one or more groups. One of these groups is distinguished from others and used in implementing accounting facilities. The positive integer corresponding to this distinguished group is termed the real group ID.
All processes have a real user ID and real group ID. These are initialized from the equivalent attributes of the process that created it.
The effective user ID and effective group ID are initially the process's real user ID and real group ID respectively. Either may be modified through execution of a set-user-ID or set-group-ID file (possibly by one its ancestors) (see execve.2
The group access list is an additional set of group ID's used only in determining resource accessibility. Access checks are performed as described below in ``File Access Permissions''.
These characters may be selected from the set of all ASCII character excluding 0 (null) and the ASCII code for / (slash). (The parity bit, bit 8, must be 0.)
Note that it is generally unwise to use *, ?, [ or ] as part of file names because of the special meaning attached to these characters by the shell.
If a path name begins with a slash, the path search begins at the root directory. Otherwise, the search begins from the current working directory. A slash by itself names the root directory. A null pathname refers to the current directory.
File access is broken down according to whether a file may be: read, written, or executed. Directory files use the execute permission to control if the directory may be searched.
File access permissions are interpreted by the system as they apply to three different classes of users: the owner of the file, those users in the file's group, anyone else. Every file has an independent set of access permissions for each of these classes. When an access check is made, the system decides if permission should be granted by checking the access information applicable to the caller.
Read, write, and execute/search permissions on a file are granted to a process if:
The process's effective user ID is that of the super-user.
The process's effective user ID matches the user ID of the owner of the file and the owner permissions allow the access.
The process's effective user ID does not match the user ID of the owner of the file, and either the process's effective group ID matches the group ID of the file, or the group ID of the file is in the process's group access list, and the group permissions allow the access.
Neither the effective user ID nor effective group ID and group access list of the process match the corresponding user ID and group ID of the file, but the permissions for ``other users'' allow access.
Otherwise, permission is denied.
A socket is an endpoint for communication between processes. Each socket has queues for sending and receiving data.
Sockets are typed according to their communications properties. These properties include whether messages sent and received at a socket require the name of the partner, whether communication is reliable, the format used in naming message recipients, etc.
Each instance of the system supports some collection of socket types; consult socket.2 for more information about the types available and their properties.
Each instance of the system supports some number of sets of communications protocols. Each protocol set supports addresses of a certain format. An Address Family is the set of addresses for a specific group of protocols. Each socket has an address chosen from the address family in which the socket was created.
Created by unroff & hp-tools. © by Hans-Peter Bischof. All Rights Reserved (1997).
Last modified 21/April/97