INTRO(2)

NAME
intro - introduction to system services and error numbers

SYNOPSIS
#include <errno.h>

DESCRIPTION

This section describes all of the system calls.

A 2V section number means one or more of the following:

•   The man page documents System V behavior only.

•   The man page documents default SunOS behavior and System V behavior as it differs from the default behavior. These System V differences are presented under SYSTEM V section headers.

•   The man page documents behavior compliant with IEEE Std 1003.1-1988 (POSIX.1).

Compile programs for the System V environment using /usr/5bin/cc. Compile programs for the default SunOS environment using /usr/bin/cc. The following man pages describe the various environments provided by Sun: lint(1V), ansic(7V), bsd(7), posix(7V), sunos(7V), svidii(7V), svidiii(7V), xopen(7V).

Most of these calls have one or more error returns. An error condition is indicated by an otherwise impossible return value. This is almost always `-1'; the individual descriptions specify the details. An error code is also made available in the external variable errno. errno is not cleared on successful calls, so it should be tested only after an error has been indicated. Note: several system calls overload the meanings of these error numbers, and the meanings must be interpreted according to the type and circumstances of the call. See ERROR CODES below for a list of system error codes.

As with normal arguments, all return codes and values from functions are of type integer unless otherwise noted.

The rest of this man page is organized as follows:

SYSTEM PARAMETERS
    System limits, values and options.

DEFINITIONS
    System abstractions and services.

STREAMS
    Modular communication between software layers (tty system, networking).

SYSTEM V IPC
    System V shared memory, semaphores, and messages.

ERROR CODES
    A list of system error codes with descriptions.

LIST OF SYSTEM CALLS
    A list of all system calls with brief descriptions.

SYSTEM PARAMETERS

Sections 2 and 3 support a naming convention for those system parameters that may change from one object to another (for example, path name length may is 255 on a UFS file system but may be 14 on an NFS file system exported by a System V based server). Typically, the system has to be queried (using pathconf(2V), fpathconf(), or sysconf(2V)) to retrieve the parameter of interest. The parameters have conceptual names such as PATH_MAX. These names are defined in header files if and only if they are invariant across all file systems and releases of the operating system, that is, very rarely. Because they may be defined and/or available from the system calls, there have to be separate names for the parameters and their values. The notation {PATH_MAX} denotes the value of the parameter PATH_MAX. Do not confuse this with _PC_PATH_MAX, the name that is passed to the system call to retrieve the value:

    maxpathlen = pathconf(".", _PC_PATH_MAX);

See pathconf(2V), and sysconf(2V) for further information about these parameters.

DEFINITIONS

  Controlling Terminal

A terminal that is associated with a session. Each session may have at most one controlling terminal; a terminal may be the controlling terminal of at most one session. The controlling terminal is used to direct signals (such as interrupts and job control signals) to the appropriate processes by way of the tty's process group. Controlling terminals are assigned when a session leader opens a terminal file that is not currently a controlling terminal.

  Descriptor

An integer assigned by the system when a file is referenced by open(2V), dup(2V), or pipe(2V) or a socket is referenced by socket(2) or socketpair(2) that uniquely identifies an access path to that file or socket from a given process or any of its children.

  Directory

A directory is a special type of file that contains entries that are references to other files. Directory entries are called links. By convention, a directory contains at least two links, `.' and `..', referred to as dot and dot-dot respectively. Dot refers to the directory itself and dot-dot refers to its parent directory.

  Effective User ID, Effective Group ID, and Access Groups

Access to system resources is governed by three values: the effective user ID, the effective group ID, and the supplementary group ID.

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 of its ancestors) (see execve(2V)).

The supplementary group ID are an additional set of group ID's used only in determining resource accessibility. Access checks are performed as described below in File Access Permissions.

  File Access Permissions

Every file in the file system has a set of access permissions. These permissions are used in determining whether a process may perform a requested operation on the file (such as opening a file for writing). Access permissions are established at the time a file is created. They may be changed at some later time through the chmod(2V) call.

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 supplementary group IDs, and the group permissions allow the access.

    Neither the effective user ID nor effective group ID and supplementary group IDs 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.

  File Name

Names consisting of up to {NAME_MAX} characters may be used to name an ordinary file, special file, or directory.

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: it is generally unwise to use *, ?, [, or ] as part of file names because of the special meaning attached to these characters by the shell. See sh(1). Although permitted, it is advisable to avoid the use of unprintable characters in file names.

  Parent Process ID
A new process is created by a currently active process fork (2V). The parent process ID of a process is the process ID of its creator.

  Path Name and Path Prefix
A path name is a null-terminated character string starting with an optional slash (/), followed by zero or more directory names separated by slashes, optionally followed by a file name. The total length of a path name must be less than {PATH_MAX} characters.

More precisely, a path name is a null-terminated character string constructed as follows:

    <path-name>::=<file-name>|<path-prefix><file-name>|/
    <path-prefix>::=<rtprefix>|/<rtprefix>
    <rtprefix>::=<dirname>/|<rtprefix><dirname>/

where <file-name> is a string of 1 to {NAME_MAX} characters other than the ASCII slash and null, and <dirname> is a string of 1 to {NAME_MAX} characters (other than the ASCII slash and null) that names a directory.

If a path name begins with a slash, the search begins at the root directory. Otherwise, the search begins at the current working directory.

A slash, by itself, names the root directory. A dot (.) names the current working directory.

A null path name also refers to the current directory. However, this is not true of all UNIX systems. (On such systems, accidental use of a null path name in routines that do not check for it may corrupt the current working directory.) For portable code, specify the current directory explicitly using `"."', rather than `""'.

  Process Group ID
Each active process is a member of a process group that is identified by a positive integer called the process group ID. This ID is the process ID of the group leader. This grouping permits the signaling of related processes (see the description of killpg() on kill(2V)) and the job control mechanisms of csh(1). Process groups exist from their creation until the last member is reaped (that is, a parent issued a call to wait(2V)).

  Process ID
Each active process in the system is uniquely identified by a positive integer called a process ID. The range of this ID is from 0 to MAXPID (see <sys/param.h>).

  Real User ID and Real Group ID
Each user on the system is identified by a positive integer termed the real user ID.

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.

  Root Directory and Current Working Directory

Each process has associated with it a concept of a root directory and a current working directory for the purpose of resolving path name searches. The root directory is used as the starting point for absolute path name resolution. The current working directory is used as the starting point for relative path name resolution. A process's root directory need not be (but typically is) the root directory of the root file system.

  Session

Each process is a member of a session. A session is associated with each controlling terminal in the system, such as login shells and windows. Each process is created in the session of its parent. A process may alter its session using setsid(2V) if it is not already a session leader. The system supports session IDs. A session leader is a process having process ID equal to process group ID equal to session ID. Only a session leader may acquire a controlling terminal. In SunOS Release 4.1, processes are created in sessions by init(8) and inetd (8C). Sessions are also created for processes that disassociate themselves from a controlling terminal using

    ioctl(fd, TIOCNOTTY, 0)

or

    setpgrp(mypid, 0) For more information about sessions, see setsid(2V).

  Signal

Signals are used for notification of asynchronous events. Signals may directed to processes, process groups, and other combinations of processes. Signals may be sent by a process or by the operating system. Some signals may be caught. There is typically a default behavior on receipt if they are not caught. For more information about signals, see signal(3V), kill(2V), sigvec(2), termio(4).

  Sockets and Address Families
A socket is an endpoint for communication between processes, similar to the way a telephone is the endpoint of communication between humans. 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.

  Special Processes

The processes with a process ID's of 0, 1, and 2 are special. Process 0 is the scheduler. Process 1 is the initialization process init, and is the ancestor of every other process in the system. It is used to control the process structure. Process 2 is the paging daemon.

  Super-user
A process is recognized as a super-user process and is granted special privileges if its effective user ID is 0.

  Tty Process Group
Each active process can be a member of a terminal group that is identified by a positive integer called the tty process group ID. This grouping is used to arbitrate between multiple jobs contending for the same terminal (see csh(1), and termio(4)), to direct signals (tty and job control) to the appropriate process group, and to terminate a group of related processes upon termination of one of the processes in the group (see exit(2V) and sigvec(2)).

STREAMS
A set of kernel mechanisms that support the development of network services and data communication drivers. It defines interface standards for character input/output within the kernel and between the kernel and user level processes. The STREAMS mechanism is composed of utility routines, kernel facilities and a set of data structures.

  Stream
A stream is a full-duplex data path within the kernel between a user process and driver routines. The primary components are a stream head, a driver and zero or more modules between the stream head and driver. A stream is analogous to a Shell pipeline except that data flow and processing are bidirectional.

  Stream Head
In a stream, the stream head is the end of the stream that provides the interface between the stream and a user process. The principle functions of the stream head are processing STREAMS-related system calls, and passing data and information between a user process and the stream.

  Driver
In a stream, the driver provides the interface between peripheral hardware and the stream. A driver can also be a pseudo-driver, such as a multiplexor or emulator, and need not be associated with a hardware device.

  Module
A module is an entity containing processing routines for input and output data. It always exists in the middle of a stream, between the stream's head and a driver. A module is the STREAMS counterpart to the commands in a Shell pipeline except that a module contains a pair of functions which allow independent bidirectional (downstream and upstream) data flow and processing.

  Downstream
In a stream, the direction from stream head to driver.

  Upstream
In a stream, the direction from driver to stream head.

  Message
In a stream, one or more blocks of data or information, with associated STREAMS control structures. Messages can be of several defined types, which identify the message contents. Messages are the only means of transferring data and communicating within a stream.

  Message Queue
In a stream, a linked list of messages awaiting processing by a module or driver.

  Read Queue
In a stream, the message queue in a module or driver containing messages moving upstream.

  Write Queue
In a stream, the message queue in a module or driver containing messages moving downstream.

  Multiplexor
A multiplexor is a driver that allows STREAMS associated with several user processes to be connected to a single driver, or several drivers to be connected to a single user process. STREAMS does not provide a general multiplexing driver, but does provide the facilities for constructing them, and for connecting multiplexed configurations of STREAMS.

SYSTEM V IPC

The SunOS system supports the System V IPC namespace. For information about shared memory, semaphores and messages see msgctl(2), msgget(2), msgop(2), semctl(2), semget(2), semop(2), shmctl(2), shmget(2) and shmop(2).

ERROR CODES

Each system call description attempts to list all possible error numbers. The following is a complete list of the error numbers and their names as given in <errno.h>. An argument list longer than 1,048,576 bytes is presented to execve(2V) or a routine that called execve(). An attempt was made to access a file in a way forbidden by the protection system. Only one usage of each address is normally permitted. Normally results from an attempt to create a socket with an address not on this machine. An attempt was made to advertise a resource which has been advertised already, or to stop the RFS while there are resources still advertised, or to force unmount a resource when it is still advertised. This error is RFS specific. An address incompatible with the requested protocol was used. For example, you should not necessarily expect to be able to use PUP Internet addresses with ARPA Internet protocols. A fork(2V) failed because the system's process table is full or the user is not allowed to create any more processes, or a system call failed because of insufficient resources. An operation was attempted on a non-blocking object that already had an operation in progress. Either a file descriptor refers to no open file, or a read (respectively, write) request is made to a file that is open only for writing (respectively, reading). During a read(2V), getmsg(2), or ioctl(2) I_RECVFD system call to a STREAMS device, something has come to the head of the queue that cannot be processed. That something depends on the system call
        read(2V)
            control information or a passed file descriptor.
        getmsg(2)
            passed file descriptor.
        ioctl(2)
            control or data information.
An attempt was made to mount a file system that was already mounted or an attempt was made to dismount a file system on which there is an active file (open file, mapped file, current directory, or mounted-on directory). A wait(2V) was executed by a process that had no existing or unwaited-for child processes. An attempt was made to send messages to a remote machine when no virtual circuit could be found. This error is RFS specific. A connection abort was caused internal to your host machine. No connection could be made because the target machine actively refused it. This usually results from trying to connect to a service that is inactive on the foreign host. A connection was forcibly closed by a peer. This normally results from the peer executing a shutdown(2) call. An attempt was made to lock a system resource that would have resulted in a deadlock situation. A required address was omitted from an operation on a socket. The argument of a function in the math library (as described in section 3M) is out of the domain of the function. A write() to an ordinary file, the creation of a directory or symbolic link, or the creation of a directory entry failed because the user's quota of disk blocks was exhausted, or the allocation of an inode for a newly created file failed because the user's quota of inodes was exhausted. An existing file was mentioned in an inappropriate context, for example, link(2V). The system encountered a hardware fault in attempting to access the arguments of a system call. The size of a file exceeded the maximum file size (1,082,201,088 bytes). A socket operation failed because the destination host was down. A socket operation was attempted to an unreachable host. This error is returned to processes that resume execution due to the removal of an identifier from the An operation that takes a long time to complete (such as a connect(2)) was attempted on a non-blocking object (see ioctl(2)). An asynchronous signal (such as interrupt or quit) that the process has elected to catch occurred during a system call. If execution is resumed after processing the signal, and the system call is not restarted, it will appear as if the interrupted system call returned this error condition. A system call was made with an invalid argument; for example, dismounting a non-mounted file system, mentioning an unknown signal in sigvec() or kill(), reading or writing a file for which lseek() has generated a negative pointer, or some other argument inappropriate for the call. Also set by math functions, see intro(3). Some physical I/O error occurred. This error may in some cases occur on a call following the one to which it actually applies. A connect() request was made on an already connected socket; or, a sendto() or sendmsg() request on a connected socket specified a destination other than the connected party. An attempt was made to write on a directory. A path name lookup involved more than 20 symbolic links. A process tried to have more open files than the system allows a process to have. The customary configuration limit is 64 per process. An attempt was made to make more than 32767 hard links to a file. A message sent on a socket was larger than the internal message buffer. An attempt was made to access remote resources which are not directly accessible. This error is RFS specific. A component of a path name exceeded 255 characters, or an entire path name exceeded 1024 characters. A socket operation encountered a dead network. The host you were connected to crashed and rebooted. A socket operation was attempted to an unreachable network. The system's table of open files is full, and temporarily no more open() calls can be accepted. An operation on a socket or pipe was not performed because the system lacked sufficient buffer space. An attempt was made to apply an inappropriate system call to a device (for example, an attempt to read a write-only device) or an attempt was made to use a device not configured by the system. This error occurs when a file name is specified and the file should exist but does not, or when one of the directories in a path name does not exist. A request is made to execute a file which, although it has the appropriate permissions, does not start with a valid magic number (see a.out(5)). A system-imposed limit on the number of simultaneous file and record locks was reached and no more were available at that time. The link (virtual circuit) connecting to a remote machine is gone. This error is RFS specific.
During an execve(2V), sbrk(), or brk(2), a program asks for more address space or swap space than the system is able to supply, or a process size limit would be exceeded. A lack of swap space is normally a temporary condition; however, a lack of address space is not a temporary condition. The maximum size of the text, data, and stack segments is a system parameter. Soft limits may be increased to their corresponding hard limits. An attempt was made to receive a message of a type that does not exist on the specified message queue; see msgop(2). A attempt was made to advertise, unadvertise, mount, or unmount remote resources while the machine has not done the proper startup to connect to the network. This error is Remote File Sharing (RFS) specific. A bad option was specified in a setsockopt() or getsockopt(2) call. A write() to an ordinary file, the creation of a directory or symbolic link, or the creation of a directory entry failed because no more disk blocks are available on the file system, or the allocation of an inode for a newly created file failed because no more inodes are available on the file system. During a STREAMS open(2V), either no STREAMS queues or no STREAMS head data structures were available. A putmsg(2) or getmsg(2) system call was attempted on a file descriptor that is not a STREAMS device. An attempt was made to use a function that is not available in this implementation. A file that is not a block device was mentioned where a block device was required, for example, in mount(2V). An request to send or receive data was disallowed because the socket is not connected. A non-directory was specified where a directory is required, for example, in a path prefix or as an argument to chdir(2V). An attempt was made to remove a directory with entries other than `&.' and `&.|.' by performing a rmdir() system call or a rename() system call with that directory specified as the target directory. Self-explanatory. The code used in an ioctl() call is not supported by the object that the file descriptor in the call refers to. I/O on a special file refers to a subdevice that does not exist, or beyond the limits of the device. It may also occur when, for example, a tape drive is not on-line or no disk pack is loaded on a drive. For example, trying to accept a connection on a datagram socket. Typically this error indicates an attempt to modify a file in some way forbidden except to its owner or super-user. It is also returned for attempts by ordinary users to do things allowed only to the super-user. The protocol family has not been configured into the system or no implementation for it exists. An attempt was made to write on a pipe or socket for which there is no process to read the data. This condition normally generates a signal; the error is returned if the signal is caught or ignored. Some protocol error occurred. This error is device specific, but is generally not related to a hardware failure. The protocol has not been configured into the system or no implementation for it exists. A protocol was specified that does not support the semantics of the socket type requested. For example, you cannot use the ARPA Internet UDP protocol with type SOCK_STREAM. The value of a function in the math library (as described in section 3M) is unrepresentable within machine precision. An attempt was made to remotely mount a file system into a path that already has a remotely mounted component. An attempt to modify a file or directory was made on a file system mounted read-only. An attempte was made to advertise a resource which is not on the local machine, or to mount/unmount a device (or pathname) that is on a remote machine. This error is RFS specific. A request to send data was disallowed because the socket had already been shut down with a previous shutdown(2) call. The support for the socket type has not been configured into the system or no implementation for it exists. An lseek() was issued to a socket or pipe. This error may also be issued for other non-seekable devices. The process or process group whose number was given does not exist, or any such process is already dead. An attempt was made to stop RFS while there are resources still mounted by remote machines. This error is RFS specific. An NFS client referenced a file that it had opened but that had since been deleted. The timer set for a STREAMS ioctl(2) call has expired. The cause of this error is device specific and could indicate either a hardware or software failure, or perhaps a timeout value that is too short for the specific operation. The status of the ioctl(2) operation is indeterminate. A connect request or an NFS request failed because the party to which the request was made did not properly respond after a period of time. (The timeout period is dependent on the communication protocol.) An attempt was made to execute a pure-procedure program that is currently open for writing, or an attempt was made to open for writing a pure-procedure program that is being executed. An operation to read disk quota information for the user failed because the system quota table was full. An operation that would cause a process to block was attempted on an object in non-blocking mode (see ioctl(2)).
A hard link to a file on another file system was attempted.

SEE ALSO
brk(2), chdir(2V), chmod(2V), connect(2), dup(2V), execve(2V), exit(2V), fork(2V), getmsg(2), getsockopt(2), ioctl(2), killpg(2), link(2V), mount(2V), msgctl(2), msgget(2), msgop(2), open(2V), pipe(2V), putmsg(2), read(2V), semctl(2), semget(2), semop(2), getsockopt(2), shmctl(2), shmget(2), shmop(2), shutdown(2), sigvec(2), socket(2), socketpair(2), wait(2V), csh(1), sh(1), intro(3), perror(3) termio(4), a.out(5)

LIST OF SYSTEM CALLS

Name Appears on Page Description