INTRO(2)INTRO(2)NAMEintro - introduction to system calls and error numbers
SYNOPSIS
#include <errno.h>
#include <limits.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.
Many of these errors are caused by certain system or user limits being
exceeded. In the individual manual pages, these limits are enclosed in
braces (i.e. {OPEN_MAX}). The section LIMITS defines these limits,
where and how they are configured, and whether they are alterable.
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 Operation not permitted
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. A special case of this involves setuid/setgid shell
scripts and a kernel that is configured with a non-zero value for
nosuidshells (the shipped default). The kernel returns EPERM when a
non-superuser attempts to execute such a shell script with a uid or
gid which is different than the user's effective uid/gid. The
kernel also returns EPERM if it has been configured with a non-zero
value for restricted_chown . Only the super-user can change the
owner of the file, because if users were able to give files away,
they could defeat the file space accounting procedures. The owner of
the file may change the group ownership only to those groups of
which he is a member. Another case where the kernel may return
EPERM is when a non-superuser tries to execute a setuid file which
belongs to some other user and the file system in which the file
resides has been mounted with the nosuid option.
2 ENOENT No such file or directory
This error occurs when a file name is specified and the file should
exist but doesn't, or when one of the directories in a path name
does not exist.
3 ESRCH No such process
No process can be found corresponding to that specified by pid in
kill(2), blockproc(2), or ptrace(2).
Page 1
INTRO(2)INTRO(2)
4 EINTR Interrupted function call
An asynchronous signal (such as interrupt or quit), which the user
has elected to catch, occurred during the execution of an
interruptible function. If execution is resumed after processing
the signal, it will appear as if the interrupted system call
returned this error condition [see section on interruptibility].
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
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.
7 E2BIG Arg list too long
An argument list longer than {ARG_MAX} bytes is presented to a
member of the exec(2) family.
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 magic number
[see a.out(4)].
9 EBADF Bad file number
Either a file descriptor refers to no open file, or a read(2)
[respectively, write(2)] request is made to a file which is open
only for writing (respectively, reading).
10 ECHILD No child processes
A wait or waitpid function was executed by a process that had no
existing or unwaited-for child processes.
11 EAGAIN Resource temporarily unavailable
1) A fork or sproc failed because the maximum number of processes
system wide {NPROC} was exceeded or the user exceeded their limit on
the number of child processes {CHILD_MAX}. 2) A system call failed
because of insufficient memory or swap space. Later calls to the
same routine may complete normally. 3) Some read system calls--
involving empty streams or locked files/records--with the O_NDELAY
flag set may return this error. See read(2). 4) An operation which
would cause a process to block was attempted on an object in non-
blocking mode [see ioctl(2)]. 5) A file system operation was unable
to complete due to a locked file or record (see fcntl(2)].
11 EWOULDBLOCK Operation would block
This is a synonym for EAGAIN.
Page 2
INTRO(2)INTRO(2)
12 ENOMEM Not enough space
During an exec(2), brk(2), or sbrk(2), a process exceeds its maximum
allowable size {PROCSIZE_MAX}. This may also be returned by device
drivers if they cannot dynamically allocate enough space.
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 system call.
15 ENOTBLK Block device required
A non-block file was mentioned where a block device was required,
(e.g., in a call to the mount(2) routine).
16 EBUSY Resource busy
An attempt was made to mount a device that was already mounted or an
attempt was made to dismount 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.
17 EEXIST File exists
An existing file was mentioned in an inappropriate context, (e.g.,
call to the link(2) routine).
18 EXDEV Improper link
A link to a file on another file system was attempted.
19 ENODEV No such device
An attempt was made to apply an inappropriate system call to a
device; e.g., read a write-only device.
20 ENOTDIR Not a directory
A non-directory was specified where a directory is required, (e.g.,
in a path prefix or as an argument to the chdir(2) routine).
21 EISDIR Is a directory
An attempt was made to write on a directory.
22 EINVAL Invalid argument
Some invalid argument (e.g., dismounting a non-mounted device;
mentioning an undefined signal in signal(2) or kill(2); reading or
writing a file for which lseek(2) has generated a negative pointer).
Also set by the math functions described in the (3M) entries of this
manual.
Page 3
INTRO(2)INTRO(2)
23 ENFILE Too many open files in system
The system file table is full (has exceeded {NFILE_MAX} entries),
and temporarily no more opens can be accepted.
24 EMFILE Too many open files in a process
No process may have more than {OPEN_MAX} descriptors open at a time.
Or the maximum number of shared memory segments {SHMAT_MAX} was
exceeded.
25 ENOTTY Inappropriate I/O control operation
An attempt was made to ioctl(2) a file that is not a special
character device.
26 ETXTBSY Text file busy
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 pure-procedure program that is being executed. This
error is no longer returned, and the actions mentioned above are now
permitted.
27 EFBIG File too large
The size of a file exceeded the per process maximum file size
{FILESIZE_MAX}, or the file has more than the maximum number of
direct and indirect extents (usually indicates an extremely
fragmented filesystem; see fsr(1m) for a method to fix this).
28 ENOSPC No space left on device
During a write(2) to an ordinary file, there is no free space left
on the device.
29 ESPIPE Illegal seek
An lseek(2) was issued to a pipe or FIFO.
30 EROFS Read-only file system
An attempt to modify a file or directory was made on a device
mounted read-only.
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 or FIFO for which there is no process to read the
data.
33 EDOM Domain error
The argument of a function in the math package (3M) or other library
functions is out of the domain of the function.
34 ERANGE Result too large
The value of a function in the math package (3M) is not
representable within machine precision, or a size specified is not
Page 4
INTRO(2)INTRO(2)
large enough.
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 msgop(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)].
37-44 Reserved numbers
45 EDEADLK Resource deadlock avoided
An attempt was made to lock a system resource that would have
resulted in a deadlock situation.
46 ENOLCK No locks available
In fcntl(2) the setting or removing of record locks on a file cannot
be accomplished because the system wide maximum number of record
entries {FLOCK_MAX} has been exceeded. It can also occur when
attempting to lock a file located on an NFS mounted file system and
the appropriate NFS lock daemons are not running.
47 ECKPT Checkpoint/Restart error
A process Checkpoint/Restart (CPR) operation has failed due to
several possible fatal reasons. It can occur when an unrecoverable
critical resource is associated with the target process during a
checkpoint or restart. See cpr(1) for more detailed descriptions on
CPR and error conditions.
50-57 Reserved numbers
60 ENOSTR Not a stream device
A putmsg(2) or getmsg(2) 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(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.
63 ENOSR Out of stream resources
During a STREAMS open(2), 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.
Page 5
INTRO(2)INTRO(2)
64 Reserved
65 ENOPKG Package not installed
This error occurs when users attempt to use a system call from a
package which has not been installed.
66-70 Reserved numbers
71 EPROTO Protocol error
Some protocol error occurred. This error is device specific, but is
generally not related to a hardware failure.
74-76 Reserved numbers
77 EBADMSG Bad message
During a read(2), getmsg(2), or ioctl(2) I_RECVFD system call to a
STREAMS device, something has come to the head of the queue that
can't be processed. That something depends on the system call:
read(2) - control information or a passed file descriptor.
getmsg(2) - passed file descriptor.
ioctl(2) - control or data information.
78 ENAMETOOLONG File name too long
The size of a pathname string exceeds {PATH_MAX} , or a pathname
component was longer than {NAME_MAX} and {_POSIX_NO_TRUNC} was in
effect for that file.
79 EOVERFLOW Value too large for defined data type
This error can occur for a variety of reasons, most to do with
existing applications being compiled with data structures that
cannot handle newer expanded sizes. It also occurs often if a 32
bit program attempts to access particular data about a 64 bit
program.
The user ID or group ID of an IPC or file system object was too
large to be stored into appropriate member of the caller-provided
structure.
The size of a file system object is larger than can be represented
in an off_t. This occurs when standard 32 bit programs attempt to
access files greater than 2GB, or files greater than 2GB are
accessed across a remote file system that cannot handle that size.
80-82 Reserved numbers
83 ELIBACC Can not access a needed shared library
Trying to exec(2) an a.out that requires a shared library (to be
linked in) and the shared library doesn't exist or the user doesn't
have permission to use it. (obsolete)
Page 6
INTRO(2)INTRO(2)
84 ELIBBAD Accessing a corrupted shared library
Trying to exec(2) an a.out that requires a shared library (to be
linked in) and exec(2) could not load the shared library. The shared
library is probably corrupted. (obsolete)
85 ELIBSCN .lib section in a.out corrupted
Trying to exec(2) an a.out that requires a shared library (to be
linked in) and there was erroneous data in the .lib section of the
a.out. The .lib section tells exec(2) what shared libraries are
needed. The a.out is probably corrupted. (obsolete)
86 ELIBMAX Attempting to link in more shared libraries than system
limit
Trying to exec(2) an a.out that requires more shared libraries (to
be linked in) than the system imposed maximum {SHLIB_MAX}.
(obsolete)
87 ELIBEXEC Cannot exec a shared library directly
Trying to exec(2) a shared library directly. This is not allowed.
(obsolete)
88 Reserved number
89 ENOSYS Function not implemented
An attempt was made to use a function that is not available in this
implementation.
90 ELOOP Too many symbolic links in path name traversal
A path name lookup involved more than {SYMLINK_MAX}symboliclinks.
91 ERESTART 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
A directory with entries other than dot and dot-dot was supplied
when an empty directory was expected.
94 Reserved number
95 ENOTSOCK Socket operation on non-socket
96 EDESTADDRREQ Destination address required
A required address was omitted from an operation on a socket.
97 EMSGSIZE Inappropriate message buffer length
A message sent on a socket was larger than the internal message
buffer or some other network limit.
Page 7
INTRO(2)INTRO(2)
98 EPROTOTYPE Protocol wrong type for socket
A protocol was specified which does not support the semantics of the
socket type requested. For example, you cannot use the ARPA
Internet UDP protocol with type SOCK_STREAM.
99 ENOPROTOOPT Option not supported by protocol
A bad option was specified in a getsockopt(2) or setsockopt(2) call.
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 exists.
122 EOPNOTSUPP Operation not supported on socket
For example, trying to accept a connection on a datagram socket.
123 EPFNOSUPPORT Protocol family not supported
The protocol family has not been configured into the system or no
implementation exists.
124 EAFNOSUPPORT Address family not supported by protocol family
An address incompatible with the requested protocol was used. For
example, you shouldn't necessarily expect to be able to use PUP
Internet addresses with ARPA Internet protocols.
125 EADDRINUSE Address already in use
Only one usage of each address is normally permitted.
126 EADDRNOTAVAIL Can't assign requested address
Normally results from an attempt to create a socket with an address
not on this machine.
127 ENETDOWN Network is down
A socket operation encountered a dead network.
128 ENETUNREACH Network is unreachable
A socket operation was attempted to an unreachable network.
129 ENETRESET Network dropped connection on 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 peer executing a shutdown(2) call.
Page 8
INTRO(2)INTRO(2)
132 ENOBUFS No buffer space available
An operation on a socket or pipe performed because the system lacked
sufficient buffer space.
133 EISCONN Socket is already connected
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.
134 ENOTCONN Socket is not connected
A request to send or receive data was disallowed because the socket
was not connected.
135-142 Reserved numbers
143 ESHUTDOWN Can't send after socket shutdown
A request to send data was disallowed because the socket had already
been shut down with a previous shutdown(2) call.
144 ETOOMANYREFS Too many references: can't splice
145 ETIMEDOUT Connection timed out
A connect request failed because the connected party did not
properly respond after a period of time. (The timeout period is
dependent on the communication protocol.) [see section on
interruptibility.]
146 ECONNREFUSED Connection refused
No connection could be made because the target machine actively
refused it.
147 EHOSTDOWN Host is down
148 EHOSTUNREACH No route to host
149 EALREADY Operation already in progress
An operation was attempted on a non-blocking object which already
had an operation in progress.
150 EINPROGRESS Operation now in progress
An operation which takes a long time to complete (such as a
connect(2)) was attempted on a non-blocking object [see ioctl(2)].
151 ESTALE Stale NFS file handle
A file operation was attempted on an object in an NFS-mounted file
system where the server has rejected the file handle sent by the
client, e.g. because the file system has been unmounted on the
server. If this error keeps recurring, the filesystem may need to
be unmounted and remounted on the client.
Page 9
INTRO(2)INTRO(2)
158 ECANCELLED Cancelled
The associated asynchronous operation was canceled before
completion.
1008 ENOTSUP Not supported
IRIX does not support this feature of a standard.
1009 ENOATTR Attribute not found
Named attribute does not exist for this file.
1010 EFSCORRUPTED Filesystem is corrupted
Operation failed because the filesystem is corrupted.
1011 EWRONGFS Mount with wrong filesystem type
Mount failed because the wrong filesystem type was supplied, or
because there is no filesystem on the device.
1133 EDQUOT Disc quota exceeded
1135 ENFSREMOTE Too many levels of remote in path
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(7).
Directory
Directories organize files into a hierarchical system where directories
are the nodes in the hierarchy. A directory is a file that catalogues
the list of files, including directories (sub-directories), 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
Page 10
INTRO(2)INTRO(2)
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(7)], which is not associated with a
hardware device.
Effective User ID and Effective Group ID 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)].
File Descriptor A file descriptor is a small integer used to do 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(2), or pipe(2). The file descriptor is used as an argument by calls
such as read(2), write(2), ioctl(2), mmap(2), munmap(2), and close(2).
NOFILES is a synonym for {OPEN_MAX}.
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, and the effective group ID of the process
matches the group 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 the effective group ID of the process
does not match the group ID of the file, and the appropriate access
bit of the ``other'' portion (0007) of the file mode is set.
Otherwise, the corresponding permissions are denied.
File Name Names consisting of 1 to {NAME_MAX} characters may be used to
name an ordinary file, special file or directory.
Page 11
INTRO(2)INTRO(2)
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)]. 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.
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(2) 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_t msg_cbytes;
ulong_t msg_qnum;
ulong_t msg_qbytes;
pid_t msg_lspid;
pid_t msg_lrpid;
time_t msg_stime;
time_t msg_rtime;
time_t msg_ctime;
Page 12
INTRO(2)INTRO(2)
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_t seq; /* slot usage sequence # */
key_t key; /* key */
msg *msg_first
is a pointer to the first message on the queue.
msg *msg_last
is 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(2) operation that changed a member of
the above structure.
Message Operation Permissions In the msgop(2) and msgctl(2) system call
descriptions, the permission required for an operation is given as
"{token}", where "token" is the type of permission needed, interpreted as
follows:
Page 13
INTRO(2)INTRO(2)
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.
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. In other words, there is no
process that can handle job control signals for the process group.
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.
Page 14
INTRO(2)INTRO(2)
The entire length of a path name is limited to {PATH_MAX} characters.
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 non-existent file.
Process ID Each active process in the system is uniquely identified by a
positive value called a process ID. This value is of the type pid_t.
Parent Process ID A new process is created by a currently active process
[see fork(2) and sproc(2)]. The parent process ID of a process is the
process ID of its creator.
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. Note
that all members of a given process group are also members of the same
session, by definition. A newly created process joins the process group
of its parent.
A terminal may have a particular process group associated with it, which
allows that group access to the terminal. This process group can be set
only to process groups that are members of the terminal's session. The
process group currently associated with the terminal is referred to as
the foreground process group; all others are background process groups.
A command interpreter, such as csh(1), that supports "job control" can
allocate the terminal to different jobs, or process groups, by placing
related processes in a single process group and associating this process
group with the terminal. A terminal's associated process group may be
set or examined by a process with sufficient privileges.
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 that
is identified by a positive value 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)].
Page 15
INTRO(2)INTRO(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 by calling setpgid(2) or setsid(2).
Read Queue In a stream, the message queue in a module or driver
containing messages moving upstream.
Real User ID and Real Group ID Each user allowed on the system is
identified by a positive integer 0 to {UID_MAX} (2,147,483,647) called a
real user 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 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 of a
process need not be the root directory of the root file system.
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 [see exec(2)].
Semaphore Identifier A semaphore identifier (semid) is a unique positive
integer created by a semget(2) 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_t 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 */
Page 16
INTRO(2)INTRO(2)
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_t 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(2) operation.
sem_ctime
is the time of the last semctl(2) operation that changed a member of
the above structure.
A semaphore is a data structure called sem that contains the following
members:
ushort_t semval; /* semaphore value */
pid_t sempid; /* pid of last operation */
ushort_t semncnt; /* # awaiting semval > cval */
ushort_t semzcnt; /* # awaiting semval = 0 */
semval
is a non-negative integer which 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 zero.
Semaphore Operation Permissions In the semop(2) and semctl(2) system call
descriptions, the permission required for an operation is given as
Page 17
INTRO(2)INTRO(2)
"{token}", where "token" is the type of permission needed interpreted as
follows:
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 (006) of sem_perm.mode
is set.
Otherwise, the corresponding permissions are denied.
Sessions 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. Each session is associated with one "login"
session (windows count as logins). Any process that is not a process
group leader may create a new session and process group by calling
setsid(2), which will put the process in a new session as its only member
and as the session leader of that session. A newly created process joins
the session of its creator.
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 of the session leaves the session by calling setsid(2).
Shared Memory Identifier A shared memory identifier (shmid) is a unique
positive integer created by a shmget(2) system call. Each shmid has a
Page 18
INTRO(2)INTRO(2)
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 */
size_t shm_segsz; /* size of segment */
pid_t shm_lpid; /* pid of last operation */
pid_t shm_cpid; /* creator pid */
shmatt_t shm_nattch; /* number of current attaches */
ulong_t 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 */
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_t 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(2)
operation.
shm_nattch
is the number of processes that currently have this segment
attached.
shm_atime
is the time of the last shmat(2) operation,
shm_dtime
is the time of the last shmdt(2) operation.
Page 19
INTRO(2)INTRO(2)
shm_ctime
is the time of the last shmctl(2) operation that changed one of the
members of the above structure.
Shared Memory Operation Permissions In the shmop(2) and shmctl(2) 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 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 processes with a process ID of 0 and a process ID
of 1 are special processes and are referred to as proc0 and proc1.
Proc0 is the 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.
Page 20
INTRO(2)INTRO(2)
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.
Supplementary Group ID A process has up to {NGROUPS_MAX} supplementary
group IDs used in determining file access permissions, in addition to the
effective group ID. The supplementary group IDs of a process are set to
the supplementary group IDs of the parent process when the process is
created.
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.
LIMITS
The various limits can be categorized as follows: not modifiable,
modifiable at sysgen time and modifiable at runtime. Most limits are
controlled by variables that can be changed by editing the file
/var/sysgen/stune or using the systune(1M) command. All the tunable
parameters and their ranges are located in the directory
/var/sysgen/mtune. Files in this directory should not be modified.
Limits may apply system wide or per process. Most per process limits are
inherited on fork, sproc, and exec. Some per process limits are managed
via the setrlimit(2) resource management call. These resource limits
have two values associated with them - a current and a maximum. A non-
privileged process may change its current value as long as its less than
the maximum. It may also lower its maximum, but once it does so, it may
not raise it again. A privileged process may raise or lower both its
current and maximum values. Resource limits may be queried
programmatically via getrlimit(2) and via the shell limit or ulimit
built-in command. They may also be set either programmatically or via
the shell. The initial values (those given to process 1, and via
inheritance to all other processes) may be set at sysgen time.
Page 21
INTRO(2)INTRO(2)
{NPROC} is the maximum number of processes allowed to run concurrently on
the system. It is modifiable at sysgen time by setting the variable
nproc within the range defined in /var/sysgen/mtune/kernel. The current
number in use and the current configured number may be retrieved via the
sar -v command.
{NFILE_MAX} is the maximum number of open files that can be
simultaneously active system wide. This is limited only by the amount of
memory in the system. The current number in use and the maximum number
that has ever been allocated may be retrieved via the sar -v command.
{FLOCK_MAX} is the maximum number of file locks system wide that may be
active. This is limited only by the amount of memory in the system. The
current number in use and the maximum number that has ever been allocated
may be retrieved via the sar -v command.
{NAME_MAX} is the maximum length of a file name. It is defined in
limits.h and is not modifiable.
{PATH_MAX} is the maximum length of a path name. It is defined in
limits.h and is not modifiable.
{LINK_MAX} is the maximum number of hard links that may be made to a
given file. It is defined in limits.h and is not modifiable.
{OPEN_MAX} is the maximum number of open files a given process may have.
The minimum value this can have is defined in limits.h. It is the
resource limit RLIMIT_NOFILE defined in setrlimit (2). The initial
current and maximum limits may be changed by setting the variables
rlimit_nofile_cur and rlimit_nofile_max within the range defined in
/var/sysgen/mtune/kernel. The current number of open files configured
may be obtained programmatically via getrlimit(2), getdtablesize(2),
sysconf(2), or ulimit(2); and may be obtained from the shell by either
the limit or ulimit built-in command.
{CHILD_MAX} is the maximum number of processes a given user may have
running simultaneously. The minimum value this can have is defined in
limits.h. It is modifiable at runtime by setting the variable maxup
within the range defined in /var/sysgen/mtune/kernel. The current
configured maximum may be obtained from sysconf(2).
Page 22
INTRO(2)INTRO(2)
{SHLIB_MAX} is the maximum number of shared libraries a program can link
with. It is modifiable at runtime by setting the variable shlbmax within
the range defined in /var/sysgen/mtune/kernel.
{ARG_MAX} is the maximum number of bytes that may be passed via exec.
The minimum value this can have is defined in limits.h. It is modifiable
at runtime by setting the variable ncargs within the range defined in
/var/sysgen/mtune/kernel. The current configured maximum may be obtained
from sysconf(2).
{FILESIZE_MAX} is the maximum size in bytes that a single file can grow
to. It is the resource limit RLIMIT_FSIZE defined in setrlimit (2). The
initial current and maximum limits may be changed by setting the
variables rlimit_fsize_cur and rlimit_fsize_max within the range defined
in /var/sysgen/mtune/kernel.
{PROCSIZE_MAX} is the maximum virtual size a process can grow to. A
process is made up an arbitrary number of virtual spaces. There are
limits on the total size of process as well as certain limits on
individual spaces. The overall limit is defined by the resource limit
RLIMIT_VMEM. The initial current and maximum limits may be changed by
setting the variables rlimit_vmem_cur and rlimit_vmem_max within the
range defined in /var/sysgen/mtune/kernel. The maximum stack size is
defined by the resource limit RLIMIT_STACK. The initial current and
maximum limits may be changed by setting the variables rlimit_stack_cur
and rlimit_stack_max within the range defined in
/var/sysgen/mtune/kernel. The maximum data size is defined by the
resource limit RLIMIT_DATA. The initial current and maximum limits may
be changed by setting the variables rlimit_data_cur and rlimit_data_max
within the range defined in /var/sysgen/mtune/kernel. The maximum size
of a shared memory segment is modifiable at sysgen time by setting the
variable shmmax within the range defined in /var/sysgen/mtune/shm.
{SHMSEG_MAX} is the maximum number of shared memory segments system wide.
It is modifiable at sysgen time by setting the variable shmmni within the
range defined in /var/sysgen/mtune/shm.
{SHMAT_MAX} is the maximum number of shared memory segments a given
process may attach to. It is modifiable at sysgen time by setting the
variable sshmseg within the range defined in /var/sysgen/mtune/shm.
{SYMLINK_MAX} is the maximum number of symbolic links a given path name
traversal will follow before assuming there is a loop. It is modifiable
at runtime by setting the variable maxsymlinks within the range defined
in /var/sysgen/mtune/kernel.
Page 23
INTRO(2)INTRO(2)
{PLOCK_MAX} is the maximum number of pages a non-privileged process is
allowed to lock at any one time. It is modifiable at runtime by setting
the variable maxlkmem within the range defined in
/var/sysgen/mtune/kernel.
{PROFIL_MAX} is the maximum number of prof structures that can be passed
as an argument to the sprofil (2) system call. It is modifiable at
sysgen time by setting the variable nprofile within the range defined in
/var/sysgen/mtune/kernel.
{IOV_MAX} is the maximum number of iovec structures that can be passed to
readv or writev. Currently, its value is 16.
INTERRUPTIBILITY
Certain system calls can be interrupted by the process receiving a
signal. These include but are not limited to fcntl(2), open(2), read(2),
write(2), and ioctl(2). The conditions under which a given system call
can be interrupted are listed on each manual page. In addition, any file
system oriented system call can either time out ( ETIMEDOUT or be
interrupted EINTR ) if the object of the system call is located on a
remote system accessed via NFS. Whether these system calls can time out
or be interrupted is based on how the underlying file system was mounted
on the local machine [see fstab(4) and mount(1M)].
All system calls can be automatically restarted upon receipt of a signal.
Whether a system call should be restarted is configurable on a per signal
basis (see sigaction(2)).
SEE ALSOsar(1), lboot(1M), mount(1M), getrlimit(2), pathconf(2), sysconf(2),
ulimit(2), intro(3), perror(3), fstab(4).
Page 24
