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man Pages(2): System Calls
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NAME

Intro, intro - introduction to system calls and error numbers

SYNOPSIS

#include <errno.h>

DESCRIPTION

This section describes all of the system calls. Most of these calls have one or more error returns. An error condition is indicated by an otherwise impossible returned value. This is almost always -1 or the null pointer; the individual descriptions specify the details. An error number 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.
In the case of multithreaded applications, the _REENTRANT flag must be defined on the command line at compilation time (-D_REENTRANT ). When the _REENTRANT flag is defined, errno becomes a macro which enables each thread to have its own errno. This errno macro can be used on either side of the assignment, just as if it were a variable.
Applications should use bound threads rather than the _lwp_* system calls (see thr_create(3T)). Using LWPs (lightweight processes) directly is not advised because libraries are only safe to use with threads, not LWPs.
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 defined in <errno.h>.
1 EPERM Not superuser
Typically this error indicates an attempt to modify a file in some way forbidden except to its owner or the super-user. It is also returned for attempts by ordinary users to do things allowed only to the super-user.
2 ENOENT No such file or directory
A file name is specified and the file should exist but doesn't, or one of the directories in a path name does not exist.
3 ESRCH No such process, LWP, or thread
No process can be found in the system that corresponds to the specified PID, LWPID_t, or thread_t.
4 EINTR Interrupted system call
An asynchronous signal (such as interrupt or quit), which the user has elected to catch, occurred during a system service routine. If execution is resumed after processing the signal, it will appear as if the interrupted routine call returned this error condition.
In a multi-threaded application, EINTR may be returned whenever another thread or LWP calls fork(2).
5 EIO I/O error
Some physical I/O error has occurred. This error may in some cases occur on a call following the one to which it actually applies.
6 ENXIO No such device or address
I/O on a special file refers to a subdevice which does not exist, or exists beyond the limit 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.
7 E2BIG Arg list too long
An argument list longer than ARG_MAX bytes is presented to a member of the exec family of routines. The argument list limit is the sum of the size of the argument list plus the size of the environment's exported shell variables.
8 ENOEXEC Exec format error
A request is made to execute a file which, although it has the appropriate permissions, does not start with a valid format (see a.out (4)).
9 EBADF Bad file number
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).
10 ECHILD No child processes
A wait routine was executed by a process that had no existing or unwaited-for child processes.
11 EAGAIN No more processes, or no more LWPs
For example, the fork routine 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 memory or swap space.
12 ENOMEM Not enough space
During execution of an exec, brk, or sbrk routine, a program asks for more space than the system is able to supply. This is not a temporary condition; the maximum size is a system parameter. On some architectures, the error may also occur if the arrangement of text, data, and stack segments requires too many segmentation registers, or if there is not enough swap space during the fork routine. If this error occurs on a resource associated with Remote File Sharing (RFS ),it indicates a memory depletion which may be temporary, dependent on system activity at the time the call was invoked.
13 EACCES Permission denied
An attempt was made to access a file in a way forbidden by the protection system.
14 EFAULT Bad address
The system encountered a hardware fault in attempting to use an argument of a routine. For example, errno potentially may be set to EFAULT any time a routine that takes a pointer argument is passed an invalid address, if the system can detect the condition. Because systems will differ in their ability to reliably detect a bad address, on some implementations passing a bad address to a routine will result in undefined behavior.
15 ENOTBLK Block device required
A non-block device or file was mentioned where a block device was required (for example, in a call to the mount routine).
16 EBUSY Device busy
An attempt was made to mount a device that was already mounted or an attempt was made to unmount a device on which there is an active file (open file, current directory, mounted-on file, active text segment). It will also occur if an attempt is made to enable accounting when it is already enabled. The device or resource is currently unavailable. EBUSY is also used by mutexes, semaphores, condition variables, and r/w locks, to indicate that a lock is held. And, EBUSY is also used by the processor control function P_ONLINE .
17 EEXIST File exists
An existing file was mentioned in an inappropriate context (for example, call to the link routine).
18 EXDEV Cross-device link
A hard link to a file on another device was attempted.
19 ENODEV No such device
An attempt was made to apply an inappropriate operation to a device (for example, read a write-only device).
20 ENOTDIR Not a directory
A non-directory was specified where a directory is required (for example, in a path prefix or as an argument to the chdir routine).
21 EISDIR Is a directory
An attempt was made to write on a directory.
22 EINVAL Invalid argument
An invalid argument was specified (for example, unmounting a non-mounted device), mentioning an undefined signal in a call to the signal or kill routine.
23 ENFILE File table overflow
The system file table is full (that is, SYS_OPEN files are open, and temporarily no more files can be opened).
24 EMFILE Too many open files
No process may have more than OPEN_MAX file descriptors open at a time.
25 ENOTTY Inappropriate ioctl for device
A call was made to the ioctl routine specifying a file that is not a special character device.
26 ETXTBSY Text file busy (obsolete)
An attempt was made to execute a pure-procedure program that is currently open for writing. Also an attempt to open for writing or to remove a pureprocedure program that is being executed. (This message is obsolete.)
27 EFBIG File too large
The size of the file exceeded the limit specified by resource RLIMIT_FSIZE; the file size exceeds the maximum supported by the file system; or the file size exceeds the offset maximum of the file descriptor. See the File Descriptor subsection of the DEFINITIONS section below.
28 ENOSPC No space left on device
While writing an ordinary file or creating a directory entry, there is no free space left on the device. In the fcntl routine, the setting or removing of record locks on a file cannot be accomplished because there are no more record entries left on the system.
29 ESPIPE Illegal seek
A call to the lseek routine was issued to a pipe.
30 EROFS Read-only file system
An attempt to modify a file or directory was made on a device mounted readonly.
31 EMLINK Too many links
An attempt to make more than the maximum number of links, LINK_MAX ,to a file.
32 EPIPE Broken pipe
A write on a pipe for which there is no process to read the data. This condition normally generates a signal; the error is returned if the signal is ignored.
33 EDOM Math argument out of domain of func
The argument of a function in the math package (3M) is out of the domain of the function.
34 ERANGE Math result not representable
The value of a function in the math package (3M) is not representable within machine precision.
35 ENOMSG No message of desired type
An attempt was made to receive a message of a type that does not exist on the specified message queue (see msgrcv(2)).
36 EIDRM Identifier removed
This error is returned to processes that resume execution due to the removal of an identifier from the file system's name space (see msgctl(2), semctl(2), and shmctl(2)).
37 ECHRNG Channel number out of range
38 EL2NSYNC Level 2 not synchronized
39 EL3HLT Level 3 halted
40 EL3RST Level 3 reset
41 ELNRNG Link number out of range
42 EUNATCH Protocol driver not attached
43 ENOCSI No CSI structure available
44 EL2HLT Level 2 halted
45 EDEADLK Deadlock condition
A deadlock situation was detected and avoided. This error pertains to file and record locking, and also applies to mutexes, semaphores, condition variables, and r/w locks.
46 ENOLCK No record locks available
There are no more locks available. The system lock table is full (see fcntl(2)).
47 ECANCELED Operation canceled
The associated asynchronous operation was canceled before completion.
48 ENOTSUP Not supported
This version of the system does not support this feature. Future versions of the system may provide support.
49 EDQUOT Disc quota exceeded
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.
58 -59
Reserved
60 ENOSTR Device not a stream
A putmsg or getmsg system call was attempted on a file descriptor that is not a STREAMS device.
61 ENODATA No data available
62 ETIME Timer expired
The timer set for a STREAMS ioctl 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 operation is indeterminate. This is also returned in the case of _lwp_cond_timedwait( ) or cond_timedwait( ).
63 ENOSR Out of stream resources
During a STREAMS open, either no STREAMS queues or no STREAMS head data structures were available. This is a temporary condition; one may recover from it if other processes release resources.
64 ENONET Machine is not on the network
This error is Remote File Sharing (RFS )specific. It occurs when users try to advertise, unadvertise, mount, or unmount remote resources while the machine has not done the proper startup to connect to the network.
65 ENOPKG Package not installed
This error occurs when users attempt to use a system call from a package which has not been installed.
66 EREMOTE Object is remote
This error is RFS -specific. It occurs when users try to advertise a resource which is not on the local machine, or try to mount/unmount a device (or pathname) that is on a remote machine.
67 ENOLINK Link has been severed
This error is RFS -specific. It occurs when the link (virtual circuit) connecting to a remote machine is gone.
68 EADV Advertise error
This error is RFS -specific. It occurs when users try to advertise a resource which has been advertised already, or try to stop RFS while there are resources still advertised, or try to force unmount a resource when it is still advertised.
69 ESRMNT Srmount error
This error is RFS -specific. It occurs when an attempt is made to stop RFS while resources are still mounted by remote machines, or when a resource is readvertised with a client list that does not include a remote machine that currently has the resource mounted.
70 ECOMM Communication error on send
This error is RFS -specific. It occurs when the current process is waiting for a message from a remote machine, and the virtual circuit fails.
71 EPROTO Protocol error
Some protocol error occurred. This error is device-specific, but is generally not related to a hardware failure.
74 EMULTIHOP Multihop attempted
This error is RFS -specific. It occurs when users try to access remote resources which are not directly accessible.
76 EDOTDOT Error 76
This error is RFS -specific. A way for the server to tell the client that a process has transferred back from mount point.
77 EBADMSG Not a data message
During a read ,getmsg, or ioctl I_RECVFD system call to a STREAMS device, something has come to the head of the queue that can not be processed. That something depends on the system call:
read :
control information or passed file descriptor.
getmsg:
passed file descriptor.
ioctl:
control or data information.
78 ENAMETOOLONG File name too long
The length of the path argument exceeds PATH_MAX ,or the length of a path component exceeds NAME_MAX while _POSIX_NO_TRUNC is in effect; see limits(4).
79 EOVERFLOW
Value too large for defined data type.
80 ENOTUNIQ Name not unique on network
Given log name not unique.
81 EBADFD File descriptor in bad state
Either a file descriptor refers to no open file or a read request was made to a file that is open only for writing.
82 EREMCHG Remote address changed
83 ELIBACC Cannot access a needed shared library
Trying to exec an a.out that requires a static shared library and the static shared library does not exist or the user does not have permission to use it.
84 ELIBBAD Accessing a corrupted shared library
Trying to exec an a.out that requires a static shared library (to be linked in) and exec could not load the static shared library. The static shared library is probably corrupted.
85 ELIBSCN .lib section in a.out corrupted
Trying to exec an a.out that requires a static shared library (to be linked in) and there was erroneous data in the .lib section of the a.out . The .lib section tells exec what static shared libraries are needed. The a.out is probably corrupted.
86 ELIBMAX Attempting to link in more shared libraries than system limit
Trying to exec an a.out that requires more static shared libraries than is allowed on the current configuration of the system. See NFS Administration Guide.
87 ELIBEXEC Cannot exec a shared library directly
Attempting to exec a shared library directly.
88 EILSEQ Error 88
Illegal byte sequence. Handle multiple characters as a single character.
89 ENOSYS Operation not applicable
90 ELOOP Number of symbolic links encountered during path name traversal exceeds
MAXSYMLINKS
91 ESTART Restartable system call
Interrupted system call should be restarted.
92 ESTRPIPE If pipe/FIFO, don't sleep in stream head
Streams pipe error (not externally visible).
93 ENOTEMPTY Directory not empty
94 EUSERS Too many users
95 ENOTSOCK Socket operation on non-socket
96 EDESTADDRREQ Destination address required
A required address was omitted from an operation on a transport endpoint. Destination address required.
97 EMSGSIZE Message too long
A message sent on a transport provider was larger than the internal message buffer or some other network limit.
98 EPROTOTYPE Protocol wrong type for socket
A protocol was specified that does not support the semantics of the socket type requested.
99 ENOPROTOOPT Protocol not available
A bad option or level was specified when getting or setting options for a protocol.
120 EPROTONOSUPPORT Protocol not supported
The protocol has not been configured into the system or no implementation for it exists.
121 ESOCKTNOSUPPORT Socket type not supported
The support for the socket type has not been configured into the system or no implementation for it exists.
122 EOPNOTSUPP Operation not supported on transport endpoint
For example, trying to accept a connection on a datagram transport endpoint.
123 EPFNOSUPPORT Protocol family not supported
The protocol family has not been configured into the system or no implementation for it exists. Used for the Internet protocols.
124 EAFNOSUPPORT Address family not supported by protocol family
An address incompatible with the requested protocol was used.
125 EADDRINUSE Address already in use
User attempted to use an address already in use, and the protocol does not allow this.
126 EADDRNOTAVAIL Cannot assign requested address
Results from an attempt to create a transport endpoint with an address not on the current machine.
127 ENETDOWN Network is down
Operation encountered a dead network.
128 ENETUNREACH Network is unreachable
Operation was attempted to an unreachable network.
129 ENETRESET Network dropped connection because of reset
The host you were connected to crashed and rebooted.
130 ECONNABORTED Software caused connection abort
A connection abort was caused internal to your host machine.
131 ECONNRESET Connection reset by peer
A connection was forcibly closed by a peer. This normally results from a loss of the connection on the remote host due to a timeout or a reboot.
132 ENOBUFS No buffer space available
An operation on a transport endpoint or pipe was not performed because the system lacked sufficient buffer space or because a queue was full.
133 EISCONN Transport endpoint is already connected
A connect request was made on an already connected transport endpoint; or, a sendto or sendmsg request on a connected transport endpoint specified a destination when already connected.
134 ENOTCONN Transport endpoint is not connected
A request to send or receive data was disallowed because the transport endpoint is not connected and (when sending a datagram) no address was supplied.
143 ESHUTDOWN Cannot send after transport endpoint shutdown
A request to send data was disallowed because the transport endpoint has already been shut down.
144 ETOOMANYREFS Too many references: cannot splice
145 ETIMEDOUT Connection timed out
A connect or send request failed because the connected party did not properly respond after a period of time; or a write or fsync request failed because a file is on an NFS file system mounted with the soft option.
146 ECONNREFUSED Connection refused
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 remote host.
147 EHOSTDOWN Host is down
A transport provider operation failed because the destination host was down.
148 EHOSTUNREACH No route to host
A transport provider operation was attempted to an unreachable host.
149 EALREADY Operation already in progress
An operation was attempted on a non-blocking object that already had an operation in progress.
150 EINPROGRESS Operation now in progress
An operation that takes a long time to complete (such as a connect) was attempted on a non-blocking object.
151 ESTALE Stale NFS file handle

DEFINITIONS

Background Process Group

Any process group that is not the foreground process group of a session that has established a connection with a controlling terminal.

Controlling Process

A session leader that established a connection to a controlling terminal.

Controlling Terminal

A terminal that is associated with a session. Each session may have, at most, one controlling terminal associated with it and a controlling terminal may be associated with only one session. Certain input sequences from the controlling terminal cause signals to be sent to process groups in the session associated with the controlling terminal; see termio (7I).

Directory

Directories organize files into a hierarchical system where directories are the nodes in the hierarchy. A directory is a file that catalogs the list of files, including directories (subdirectories), that are directly beneath it in the hierarchy. Entries in a directory file are called links. A link associates a file identifier with a filename. By convention, a directory
contains at least two links, . (dot) and .. (dot-dot). The link called dot refers to the directory itself while dot-dot refers to its parent directory. The root directory, which is the top-most node of the hierarchy, has itself as its parent directory. The pathname of the root directory is / and the parent directory of the root directory is /.

Downstream

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

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 log driver (see log(7D)), which is not associated with a hardware device.

Effective User ID and

An active process has an effective user ID and an effective group ID that are used to determine file access permissions (see below). The effective user ID and effective group ID are equal to the process's real user ID and real group ID ,respectively, unless the process or one of its ancestors evolved from a file that had the set-user-ID bit or set-group-ID bit set (see exec(2)).

Effective Group ID

File Access Permissions

Read, write, and execute/search permissions on a file are granted to a process if one or more of the following are true:
The effective user ID of the process is super-user.
The effective user ID of the process matches the user ID of the owner of the file and the appropriate access bit of the "owner" portion (0700) of the file mode is set.
The effective user ID of the process does not match the user ID of the owner of the file, but either the effective group ID or one of the supplementary group ID sof the process match the group ID of the file and the appropriate access bit of the "group" portion (0070) of the file mode is set.
The effective user ID of the process does not match the user ID of the owner of the file, and neither the effective group ID nor any of the supplementary group ID sof the process match the group ID of the file, but the appropriate access bit of the "other" portion (0007) of the file mode is set.
Otherwise, the corresponding permissions are denied.

File Descriptor

A file descriptor is a small integer used to perform I/O on a file. The value of a file descriptor is from 0 to (NOFILES-1 ). A process may have no more than NOFILES file descriptors open simultaneously. A file descriptor is returned by system calls such as open( ) or pipe( ). The file descriptor is used as an argument by calls such as read ,write, ioctl, and close.
Each file descriptor has a corresponding offset maximum. For regular files that were opened without setting the O_LARGEFILE flag, the offset maximum is 2 Gbyte - 1 byte 31 (2 -1 bytes). For regular files that were opened with the O_LARGEFILE flag set, the 63 offset maximum is 2 -1 bytes.

File Name

Names consisting of 1 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 character values excluding \0 (null) and the ASCII code for / (slash).
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 (see sh(1), csh(1), and ksh(1)). Although permitted, the use of unprintable characters in file names should be avoided.
A file name is sometimes referred to as a pathname component. The interpretation of a pathname component is dependent on the values of NAME_MAX and _POSIX_NO_TRUNC associated with the path prefix of that component. If any pathname component is longer than NAME_MAX and _POSIX_NO_TRUNC is in effect for the path prefix of that component (see fpathconf(2) and limits(4)), it shall be considered an error condition in that implementation. Otherwise, the implementation shall use the first NAME_MAX bytes of the pathname component.

Foreground Process Group

Each session that has established a connection with a controlling terminal will distinguish one process group of the session as the foreground process group of the controlling terminal. This group has certain privileges when accessing its controlling terminal that are denied to background process groups.

{IOV_MAX}

Maximum number of entries in a struct iovec array.

{LIMIT}

The braces notation, {LIMIT}, is used to denote a magnitude limitation imposed by the implementation. This indicates a value which may be defined by a header file (without the braces), or the actual value may be obtained at runtime by a call to the configuration inquiry pathconf(2) with the name argument _PC_LIMIT .

Masks

The file mode creation mask of the process used during any create function calls to turn off permission bits in the mode argument supplied. Bit positions that are set in umask(cmask) are cleared in the mode of the created file.

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.

Message Queue Identifier

A message queue identifier (msqid) is a unique positive integer created by a msgget system call. Each msqid has a message queue and a data structure associated with it. The data structure is referred to as msqid_ds and contains the following members:
struct     ipc_perm msg_perm;
struct     msg * msg_first;
struct     msg * msg_last;
ulong      msg_cbytes;


ulong      msg_qnum;
ulong      msg_qbytes;
pid_t      msg_lspid;
pid_t      msg_lrpid;
time_t     msg_stime;
time_t     msg_rtime;
time_t     msg_ctime;
Here are descriptions of the fields of the msqid_ds structure:
msg_perm is an ipc_perm structure that specifies the message operation permission (see below). This structure includes the following members:
uid_t      cuid;     /* creator user id * /
gid_t      cgid;     /* creator group id * /
uid_t      uid;      /* user id * /
gid_t      gid;      /* group id * /
mode_t     mode;     /* r/w permission * /
ulong      seq;      /* slot usage sequence # * /
key_t      key;      /* key * /
* msg_firstis a pointer to the first message on the queue.
* msg_lastis a pointer to the last message on the queue.
msg_cbytes is the current number of bytes on the queue.
msg_qnum is the number of messages currently on the queue.
msg_qbytes is the maximum number of bytes allowed on the queue.
msg_lspid is the process ID of the last process that performed a msgsnd operation.
msg_lrpid is the process id of the last process that performed a msgrcv operation.
msg_stime is the time of the last msgsnd operation.
msg_rtime is the time of the last msgrcv operation
msg_ctime is the time of the last msgctl operation that changed a member of the above structure.

Message Operation Permissions

In the msgop and msgctl system call descriptions, the permission required for an operation is given as {token}, where token is the type of permission needed, interpreted as follows:
00400     READ by user
00200     WRITE by user
00040     READ by group
00020     WRITE by group
00004     READ by others
00002     WRITE by others
Read and write permissions on a msqid are granted to a process if one or more of the following are true:
The effective user ID of the process is super-user.
The effective user ID of the process matches msg_perm.cuid or msg_perm.uid in the data structure associated with msqid and the appropriate bit of the "user" portion (0600) of msg_perm.mode is set.
The effective group ID of the process matches msg_perm.cgid or msg_perm.gid and the appropriate bit of the "group" portion (060) of msg_perm.mode is set.
The appropriate bit of the "other" portion (006) of msg_perm.mode is set.
Otherwise, the corresponding permissions are denied.

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.

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.

Offset Maximum

An offset maximum is an attribute of an open file description representing the largest value that can be used as a file offset.

Orphaned Process Group

A process group in which the parent of every member in the group is either itself a member of the group, or is not a member of the process group's session.

Path Name

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.
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.
Unless specifically stated otherwise, the null path name is treated as if it named a nonexistent file.

Process ID

Each process in the system is uniquely identified during its lifetime by a positive integer called a process ID . A process ID may not be reused by the system until the process lifetime, process group lifetime, and session lifetime ends for any process ID ,process group ID ,and session ID equal to that process ID . Within a process, there are threads with thread id's, called thread_t and LWPID_t. These threads are not visible to the outside process.

Parent Process ID

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

Privilege

Having appropriate privilege means having the capability to override system restrictions.

Process Group

Each process in the system is a member of a process group that is identified by a process group ID . Any process that is not a process group leader may create a new process group and become its leader. Any process that is not a process group leader may join an existing process group that shares the same session as the process. A newly created process joins the process group of its parent.

Process Group Leader

A process group leader is a process whose process ID is the same as its process group ID .

Process Group ID

Each active process is a member of a process group and 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 kill(2)).

Process Lifetime

A process lifetime begins when the process is forked and ends after it exits, when its termination has been acknowledged by its parent process. See wait(2).

Process Group Lifetime

A process group lifetime begins when the process group is created by its process group leader, and ends when the lifetime of the last process in the group ends or when the last process in the group leaves the group.

Processor Set ID

The processors in a system may be divided into subsets, known as processor sets. A process bound to one of these sets will run only on processors in that set, and the processors in the set will normally run only processes that have been bound to the set. Each active processor set is identified by a positive integer. See pset_create(2).

Read Queue

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

Real User ID and Real

Each user allowed on the system is identified by a positive integer (0 to MAXUID )called a real user ID .

Group ID

Each user is also a member of a group. The group is identified by a positive integer called the real group ID .
An active process has a real user ID and real group ID that are set to the real user ID and real group ID ,respectively, of the user responsible for the creation of the process.

Root Directory and Current Working

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 of a process need not be the root directory of the root file system.

Directory

Saved Resource Limits

Saved resource limits is an attribute of a process that provides some flexibility in the handling of unrepresentable resource limits, as described in the exec family of functions and setrlimit(2).

Saved User ID and Saved Group ID

The saved user ID and saved group ID are the values of the effective user ID and effective group ID prior to an exec of a file whose set user or set group file mode bit has been set (see exec(2)).

Semaphore Identifier

A semaphore identifier (semid) is a unique positive integer created by a semget system call. Each semid has a set of semaphores and a data structure associated with it. The data structure is referred to as semid_ds and contains the following members:
struct     ipc_perm sem_perm;      /* operation permission struct * /
struct     sem * sem_base;         /* ptr to first semaphore in set * /
ushort     sem_nsems;              /* number of sems in set * /
time_t     sem_otime;              /* last operation time * /
time_t     sem_ctime;              /* last change time * /
                                   /* Times measured in secs since * /
                                   /* 00:00:00 GMT, Jan. 1, 1970 * /
Here are descriptions of the fields of the semid_ds structure:
sem_perm is an ipc_perm structure that specifies the semaphore operation permission (see below). This structure includes the following members:
uid_t      uid;      /* user id * /
gid_t      gid;      /* group id * /
uid_t      cuid;     /* creator user id * /
gid_t      cgid;     /* creator group id * /
mode_t     mode;     /* r/a permission * /
ulong      seq;      /* slot usage sequence number * /
key_t      key;      /* key * /
sem_nsems is equal to the number of semaphores in the set. Each semaphore in the set is referenced by a nonnegative integer referred to as a sem_num. sem_num values run sequentially from 0 to the value of sem_nsems minus 1.
sem_otime is the time of the last semop operation.
sem_ctime is the time of the last semctl operation that changed a member of the above structure.
A semaphore is a data structure called sem that contains the following members:
ushort     semval;      /* semaphore value * /
pid_t      sempid;      /* pid of last operation * /
ushort     semncnt;     /* # awaiting semval > cval * /
ushort     semzcnt;     /* # awaiting semval = 0 * /
semval is a non-negative integer that is the actual value of the semaphore.
sempid is equal to the process ID of the last process that performed a semaphore operation on this semaphore.
semncnt is a count of the number of processes that are currently suspended awaiting this semaphore's semval to become greater than its current value.
semzcnt is a count of the number of processes that are currently suspended awaiting this semaphore's semval to become 0 .

Semaphore Operation

In the semop and semctl system call descriptions, the permission required for an operation is given as {token}, where token is the type of permission needed interpreted as follows:

Permissions 

00400     READ by user
00200     ALTER by user
00040     READ by group
00020     ALTER by group
00004     READ by others
00002     ALTER by others
Read and alter permissions on a semid are granted to a process if one or more of the following are true:
The effective user ID of the process is super-user.
The effective user ID of the process matches sem_perm.cuid or sem_perm.uid in the data structure associated with semid and the appropriate bit of the "user" portion (0600) of sem_perm.mode is set.
The effective group ID of the process matches sem_perm.cgid or sem_perm.gid and the appropriate bit of the "group" portion (060) of sem_perm.mode is set.
The appropriate bit of the "other" portion (06) of sem_perm.mode is set.
Otherwise, the corresponding permissions are denied.

Session

A session is a group of processes identified by a common ID called a session ID ,capable of establishing a connection with a controlling terminal. Any process that is not a process group leader may create a new session and process group, becoming the session leader of the session and process group leader of the process group. A newly created process joins the session of its creator.

Session ID

Each session in the system is uniquely identified during its lifetime by a positive integer called a session ID ,the process ID of its session leader.

Session Leader

A session leader is a process whose session ID is the same as its process and process group ID .

Session Lifetime

A session lifetime begins when the session is created by its session leader, and ends when the lifetime of the last process that is a member of the session ends, or when the last process that is a member in the session leaves the session.

Shared Memory Identifier

A shared memory identifier (shmid) is a unique positive integer created by a shmget system call. Each shmid has a segment of memory (referred to as a shared memory segment) and a data structure associated with it. (Note that these shared memory segments must be explicitly removed by the user after the last reference to them is removed.) The data structure is referred to as shmid_ds and contains the following members:
struct ipc_perm      shm_perm;           /* operation permission struct * /
int                  shm_segsz;          /* size of segment * /
struct region        * shm_reg;          /* ptr to region structure * /
char                 pad[4];             /* for swap compatibility * /
pid_t                shm_lpid;           /* pid of last operation * /
pid_t                shm_cpid;           /* creator pid * /
ushort               shm_nattch;         /* number of current attaches * /
ushort               shm_cnattch;        /* used only for shminfo * /
time_t               shm_atime;          /* last attach time * /
time_t               shm_dtime;          /* last detach time * /
time_t               shm_ctime;          /* last change time * /
                                         /* Times measured in secs since * /
                                         /* 00:00:00 GMT, Jan. 1, 1970 * /
Here are descriptions of the fields of the shmid_ds structure:
shm_perm is an ipc_perm structure that specifies the shared memory operation permission (see below). This structure includes the following members:
uid_t      cuid;     /* creator user id * /
gid_t      cgid;     /* creator group id * /
uid_t      uid;      /* user id * /
gid_t      gid;      /* group id * /
mode_t     mode;     /* r/w permission * /
ulong      seq;      /* slot usage sequence # * /
key_t      key;      /* key * /
shm_segsz specifies the size of the shared memory segment in bytes.
shm_cpid is the process ID of the process that created the shared memory identifier.
shm_lpid is the process ID of the last process that performed a shmop operation.
shm_nattch is the number of processes that currently have this segment attached.
shm_atime is the time of the last shmat operation (see shmop(2)).
shm_dtime is the time of the last shmdt operation (see shmop(2)).
shm_ctime is the time of the last shmctl operation that changed one of the members of the above structure.

Shared Memory Operation

In the shmop and shmctl system call descriptions, the permission required for an operation is given as {token}, where token is the type of permission needed interpreted as follows:

Permissions 

00400     READ by user
00200     WRITE by user
00040     READ by group
00020     WRITE by group
00004     READ by others
00002     WRITE by others
Read and write permissions on a shmid are granted to a process if one or more of the following are true:
The effective user ID of the process is super-user.
The effective user ID of the process matches shm_perm.cuid or shm_perm.uid in the data structure associated with shmid and the appropriate bit of the "user" portion (0600) of shm_perm.mode is set.
The effective group ID of the process matches shm_perm.cgid or shm_perm.gid and the appropriate bit of the "group" portion (060) of shm_perm.mode is set.
The appropriate bit of the "other" portion (06) of shm_perm.mode is set.
Otherwise, the corresponding permissions are denied.

Special Processes

The process with ID 0 and the process with ID 1 are special processes referred to as proc0 and proc1; see kill(2). proc0 is the process scheduler. proc1 is the initialization process (init); proc1 is the ancestor of every other process in the system and is used to control the process structure.

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 principal functions of the stream head are processing STREAMS -relatedsystem calls and passing data and information between a user process and the stream.

Super-user

A process is recognized as a super-user process and is granted special privileges, such as immunity from file permissions, if its effective user ID is 0.

Upstream

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

Write Queue

In a stream, the message queue in a module or driver containing messages moving downstream.
Name                            Description
access(2)
determine accessibility of a file
acct(2)
enable or disable process accounting
acl(2)
get or set a file's Access Control List (ACL)
adjtime(2)
correct the time to allow synchronization of the system
clock
alarm(2)
set a process alarm clock
audit(2)
write a record to the audit log
auditon(2)
manipulate auditing
auditsvc(2)
write audit log to specified file descriptor
brk(2)
change the amount of space allocated for the calling
process's data segment
chdir(2)
change working directory
chmod(2)
change access permission mode of file
chown(2)
change owner and group of a file
chroot(2)
change root directory
close(2)
close a file descriptor
creat(2)
create a new file or rewrite an existing one
dup(2)
duplicate an open file descriptor
exec(2)
execute a file
execl(2)
See exec(2)
execle(2)
See exec(2)
execlp(2)
See exec(2)
execv (2)
See exec(2)
execve (2)
See exec(2)
execvp(2)
See exec(2)
_exit(2)
See exit(2)
exit(2)
terminate process
facl(2)
See acl(2)
fchdir(2)
See chdir(2)
fchmod (2)
See chmod(2)
fchown(2)
See chown(2)
fchroot(2)
See chroot(2)
fcntl(2)
file control
fork(2)
create a new process
fork1(2)
See fork(2)
fpathconf(2)
get configurable pathname variables
fstat(2)
See stat(2)
fstatvfs(2)
See statvfs(2)
getaudit(2)
get and set process audit information
getauid(2)
get and set user audit identity
getcontext(2)
get and set current user context
getdents(2)
read directory entries and put in a file system indepen-
dent format
getegid(2)
See getuid(2)
geteuid(2)
See getuid(2)
getgid(2)
See getuid(2)
getgroups(2)
get or set supplementary group access list IDs
getitimer(2)
get or set value of interval timer
getmsg(2)
get next message off a stream
getpgid (2)
See getpid(2)
getpgrp(2)
See getpid(2)
getpid(2)
get process, process group, and parent process IDs
getpmsg(2)
See getmsg(2)
getppid(2)
See getpid(2)
getrlimit(2)
control maximum system resource consumption
getsid(2)
get process group ID of session leader
getuid(2)
get real user, effective user, real group, and effective
group IDs
ioctl(2)
control device
kill(2)
send a signal to a process or a group of processes
lchown(2)
See chown(2)
link(2)
link to a file
llseek(2)
move extended read/write file pointer
lseek(2)
move read/write file pointer
lstat(2)
See stat(2)
_lwp_cond_broadcast(2)
See _lwp_cond_signal(2)
_lwp_cond_signal(2)
signal a condition variable
_lwp_cond_timedwait(2)
See _lwp_cond_wait(2)
_lwp_cond_wait(2)
wait on a condition variable
_lwp_continue(2)
See _lwp_suspend(2)
_lwp_create(2)
create a new light-weight process
_lwp_exit(2)
terminate the calling LWP
_lwp_getprivate(2)
See _lwp_setprivate(2)
_lwp_info(2)
return the time-accounting information of a single LWP
_lwp_kill(2)
send a signal to a LWP
_lwp_makecontext(2)
initialize an LWP context
_lwp_mutex_lock(2)
mutual exclusion
_lwp_mutex_trylock(2)
See _lwp_mutex_lock(2)
_lwp_mutex_unlock(2)
See _lwp_mutex_lock(2)
_lwp_self(2)
get LWP identifier
_lwp_sema_init(2)
See _lwp_sema_wait(2)
_lwp_sema_post(2)
See _lwp_sema_wait(2)
_lwp_sema_trywait(2)
See _lwp_sema_wait(2)
_lwp_sema_wait(2)
semaphore operations
_lwp_setprivate(2)
set/get LWP specific storage
_lwp_sigredirect(2)
See _signotifywait(2)
_lwp_suspend(2)
continue or suspend LWP execution
_lwp_wait(2)
wait for a LWP to terminate
memcntl(2)
memory management control
mincore(2)
determine residency of memory pages
mkdir(2)
make a directory
mknod(2)
make a directory, or a special or ordinary file
mmap(2)
map pages of memory
mount (2)
mount a file system
mprotect(2)
set protection of memory mapping
msgctl(2)
message control operations
msgget(2)
get message queue
msgrcv(2)
message receive operation
msgsnd(2)
message send operation
munmap(2)
unmap pages of memory
nice(2)
change priority of a process
ntp_adjtime(2)
adjust local clock parameters
ntp_gettime(2)
get local clock values
open(2)
open a file
pathconf(2)
See fpathconf(2)
pause(2)
suspend process until signal
pipe(2)
create an interprocess channel
poll(2)
input/output multiplexing
p_online(2)
change processor operational status
pread(2)
See read (2)
priocntl(2)
process scheduler control
priocntlset(2)
generalized process scheduler control
processor_bind(2)
bind LWPs to a processor
processor_info(2)
determine type and status of a processor
profil (2)
execution time profile
pset_assign(2)
See pset_create(2)
pset_bind(2)
bind LWPs to a set of processors
pset_create(2)
manage sets of processors
pset_destroy(2)
See pset_create(2)
pset_info(2)
get information about a processor set
ptrace(2)
allows a parent process to control the execution of a
child process
putmsg(2)
send a message on a stream
putpmsg(2)
See putmsg(2)
pwrite(2)
See write(2)
read (2)
read from file
readlink(2)
read the contents of a symbolic link
readv(2)
See read (2)
rename(2)
change the name of a file
resolvepath(2)
resolve all symbolic links of a path name
rmdir(2)
remove a directory
sbrk(2)
See brk(2)
semctl(2)
semaphore control operations
semget(2)
get set of semaphores
semop (2)
semaphore operations
setaudit(2)
See getaudit(2)
setauid(2)
See getauid(2)
setcontext(2)
See getcontext(2)
setegid(2)
See setuid(2)
seteuid(2)
See setuid(2)
setgid(2)
See setuid(2)
setgroups(2)
See getgroups(2)
setitimer(2)
See getitimer(2)
setpgid(2)
set process group ID
setpgrp(2)
set process group ID
setregid(2)
set real and effective group IDs
setreuid(2)
set real and effective user IDs
setrlimit(2)
See getrlimit(2)
setsid(2)
create session and set process group ID
setuid(2)
set user and group IDs
shmat(2)
See shmop(2)
shmctl(2)
shared memory control operations
shmdt(2)
See shmop(2)
shmget(2)
get shared memory segment identifier
shmop(2)
shared memory operations
sigaction(2)
detailed signal management
sigaltstack(2)
set or get signal alternate stack context
_signotifywait(2)
deliver process signals to specific LWPs
sigpending(2)
examine signals that are blocked and pending
sigprocmask(2)
change and/or examine caller's signal mask
sigsend(2)
send a signal to a process or a group of processes
sigsendset(2)
See sigsend(2)
sigsuspend(2)
install a signal mask and suspend caller until signal
sigwait(2)
wait until a signal is posted
stat(2)
get file status
statvfs(2)
get file system information
stime(2)
set system time and date
swapctl(2)
manage swap space
symlink(2)
make a symbolic link to a file
sync(2)
update super block
sysfs(2)
get file system type information
sysinfo(2)
get and set system information strings
time(2)
get time
times(2)
get process and child process times
uadmin(2)
administrative control
ulimit(2)
get and set process limits
umask(2)
set and get file creation mask
umount(2)
unmount a file system
uname(2)
get name of current operating system
unlink(2)
remove directory entry
ustat(2)
get file system statistics
utime(2)
set file access and modification times
utimes(2)
set file access and modification times
vfork(2)
spawn new process in a virtual memory efficient way
vhangup(2)
virtually "hangup" the current controlling terminal
wait(2)
wait for child process to stop or terminate
waitid(2)
wait for child process to change state
waitpid(2)
wait for child process to change state
write(2)
write on a file
writev(2)
See write(2)
yield(2)
yield execution to another lightweight process