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@ -1,460 +1,583 @@
.\" Copyright (c) 1980,1983,1986 Regents of the University of California.
.\" Copyright (c) 1980, 1983, 1986, 1991, 1993
.\" The Regents of the University of California.
.\" All rights reserved. The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\" @(#)intro.2 6.7 (Berkeley) 5/23/86
.\" @(#)intro.2 8.5 (Berkeley) 2/27/95
.\"
.TH INTRO 2 "June 30, 1986"
.UC 4
.de en
.HP
\\$1 \\$2 \\$3
.br
..
.SH NAME
intro, errno \- introduction to system calls and error numbers
.SH SYNOPSIS
.B "#include <errno.h>"
.SH 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 return
value. This is almost always \-1; the individual descriptions
specify the details.
Note that a number of system calls overload the meanings of these
error numbers, and that the meanings must be interpreted according
to the type and circumstances of the call.
.PP
As with normal arguments, all return codes and values from
functions are of type integer unless otherwise noted.
An error number is also made available in the external
variable \fBerrno\fP, which is not cleared
on successful calls.
Thus \fBerrno\fP should be tested only after an error has occurred.
.PP
.\" Adapted to MINIX 3
.\"
.Dd July 14, 2010
.Dt INTRO 2
.Os
.Sh NAME
.Nm intro ,
.Nm errno
.Nd introduction to system calls and error numbers
.Sh SYNOPSIS
.In errno.h
.Sh DESCRIPTION
This section provides an overview of the system calls,
their error returns, and other common definitions and concepts.
.Sh DIAGNOSTICS
Nearly all of the system calls provide an error number in the external
variable
.Va errno .
.Pp
When a system call detects an error,
it returns an integer value
indicating failure (usually \-1)
and sets the variable
.Va errno
accordingly.
(This allows interpretation of the failure on receiving
a \-1 and to take action accordingly.)
Successful calls never set
.Va errno ;
once set, it remains until another error occurs.
It should only be examined after an error has been reported, because
otherwise a leftover value from some previous error may be found
instead.
.Po
Many library functions that are not system calls also set
.Va errno
on return, in the same fashion.
In these cases a nonzero value may be left in
.Va errno
even upon successful return if some internal action failed.
.Pc
.Pp
The manual page for each system call will list some of the common
errno codes that system call can return, but that should not be
considered an exhaustive list, i.e.
a properly written program should be able to gracefully recover from
any error that a system call might return.
Documenting all the error codes that a system call can return in
a more specification-like manner would take more resources than
this project has available.
.Pp
Note also that a number of system calls overload the meanings of these
error numbers, and that in these cases the meanings must be
interpreted according to the type and circumstances of the call.
.Pp
The following is a list of the errors and their
names as given in
.RI < sys/errno.h >:
.en 0 OK "Error 0
Unused. (The symbol "OK" is only used inside the kernel source.)
.en 1 EPERM "Not owner
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.
.en 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.
.en 3 ESRCH "No such process
The process or process group whose number was given
does not exist, or any such process is already dead.
.en 4 EINTR "Interrupted system call
An asynchronous signal (such as interrupt or quit)
that the user has elected to catch
occurred during a system call.
If execution is resumed
after processing the signal
and the system call is not restarted,
it will appear as if the interrupted system call
returned this error condition.
.en 5 EIO "I/O error
Some physical I/O error occurred during an I/O operation, usually
.B read
.In errno.h .
.Bl -hang -width Ds
.It Er 0 OK Em "Error 0" .
Not used. (The symbol "OK" is only used inside the kernel source.)
.It 1 EPERM Em "Operation not permitted" .
An attempt was made to perform an operation limited to processes
with appropriate privileges or to the owner of a file or other
resources.
.It Er 2 ENOENT Em "No such file or directory" .
A component of a specified pathname did not exist, or the
pathname was an empty string.
.It Er 3 ESRCH Em "No such process" .
No process could be found corresponding to that specified by the given
process ID.
It Er 4 EINTR Em "Interrupted function call" .
An asynchronous signal (such as
.Dv SIGINT
or
.BR write .
Operations on file descriptors that refer to devices that are forcefully
taken away or in a bad state will also provoke this error.
.en 6 ENXIO "No such device or address
I/O on a special file refers to a subdevice that does not
exist,
or beyond the limits of the device.
It may also occur when, for example, an illegal tape drive
unit number is selected
or a disk pack is not loaded on a drive.
.en 7 E2BIG "Arg list too long
An argument list longer than ARG_MAX bytes is presented to
.BR execve .
ARG_MAX is set to 4096 bytes for 16-bit MINIX 3, 16384 bytes for 32-bit
MINIX 3, and unlimited for Minix-vmd as these systems are released.
.en 8 ENOEXEC "Exec format error
A request is made to execute a file
.Dv SIGQUIT )
was caught by the process during the execution of an interruptible
function.
If the signal handler performs a normal return, the
interrupted function call will seem to have returned the error condition.
.It Er 5 EIO Em "Input/output error" .
Some physical input or output error occurred.
This error will not be reported until a subsequent operation on the same file
descriptor and may be lost (over written) by any subsequent errors.
.It Er 6 ENXIO Em "Device not configured" .
Input or output on a special file referred to a device that did not
exist, or
made a request beyond the limits of the device.
This error may also occur when, for example,
a tape drive is not online or no disk pack is
loaded on a drive.
.It Er 7 E2BIG Em "Arg list too long" .
The number of bytes used for the argument and environment
list of the new process exceeded the current limit of
262144 bytes
.Pf ( Dv ARG_MAX
in
.In limits.h ) .
.It Er 8 ENOEXEC Em "Exec format error" .
A request was made to execute a file
that, although it has the appropriate permissions,
does not start with a valid magic number, (see
.BR a.out (5)).
.en 9 EBADF "Bad file number
Either a file descriptor refers to no
open file,
or a read (resp. write) request is made to
a file that is open only for writing (resp. reading).
.en 10 ECHILD "No children
.B Wait
and the process has no
living or unwaited-for children.
.en 11 EAGAIN "Resource temporarily unavailable
In a
.B fork,
the system's process table is full or the user is not allowed to create
any more processes, otherwise an operation that would cause a process to
block was attempted on an object in non-blocking mode (see \fBfcntl\fP(2)).
.en 12 ENOMEM "Not enough core
During an
.B execve
was not in the format required for an
executable file.
.It Er 9 EBADF Em "Bad file descriptor" .
A file descriptor argument was out of range, referred to no open file,
or a
.Xr read 2
(or
.Xr write 2 )
request was made to a file that was
only open for writing (or reading).
.It Er 10 ECHILD Em "\&No child processes" .
A
.Xr wait 2
or
.B brk,
a program asks for more (virtual) memory than the system is
able to supply,
or a process size limit would be exceeded.
The maximum size
of the data+stack segment is set by the
.BR chmem (1)
program. For Minix-vmd a small data+stack size is increased to 3 megabytes
when a program is executed.
.en 13 EACCES "Permission denied
.Xr waitpid 2
function was executed by a process that had no existing or unwaited-for
child processes.
.It Er 11 EAGAIN Em "Resource temporarily unavailable" .
This is a temporary condition and later calls to the
same routine may complete normally.
.It Er 12 ENOMEM Em "Cannot allocate memory" .
The new process image required more memory than was allowed by the hardware
or by system-imposed memory management constraints.
Soft limits may be increased to their corresponding hard limits.
.It Er 13 EACCES Em "Permission denied" .
An attempt was made to access a file in a way forbidden
by the protection system. Also an attempt to open a device for writing
that is physically write protected.
.en 14 EFAULT "Bad address
An argument of a system call is outside the address space allocated to a
process.
.en 15 ENOTBLK "Block device required
A plain file was mentioned where a block device was required,
e.g., in
.BR mount .
.en 16 EBUSY "Resource busy
An attempt 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, or active text segment).
A request was made to an exclusive access device that was already in use.
.en 17 EEXIST "File exists
by its file access permissions.
.It Er 14 EFAULT Em "Bad address" .
The system detected an invalid address in attempting to
use an argument of a call.
The reliable detection of this error cannot be guaranteed and when not detected
may result in the generation of a signal, indicating an address violation,
which is sent to the process.
.It Er 15 ENOTBLK Em "Block device required" .
A block device operation was attempted on a non-block device or file.
.It Er 16 EBUSY Em "Resource busy" .
An attempt to use a system resource which was in use at the time
in a manner which would have conflicted with the request.
.It Er 17 EEXIST Em "File exists" .
An existing file was mentioned in an inappropriate context,
e.g.,
.BR link .
.en 18 EXDEV "Cross-device link
A hard link to a file on another device
for instance, as the new link name in a
.Xr link 2
function.
.It Er 18 EXDEV Em "Improper link" .
A hard link to a file on another file system
was attempted.
.en 19 ENODEV "No such device
An attempt was made to access a device that is not configured by the system,
i.e., there is no driver for the device.
.en 20 ENOTDIR "Not a directory
A non-directory was specified where a directory
is required,
for example, in a path name or
as an argument to
.BR chdir .
.en 21 EISDIR "Is a directory
An attempt to write on a directory.
.en 22 EINVAL "Invalid argument
Some invalid argument:
dismounting a non-mounted
device,
mentioning an unknown signal in
.B signal,
or some other argument inappropriate for the call.
Also set by math functions, (see
.BR math (3)).
.en 23 ENFILE "File table overflow
The system's table of open files is full,
and temporarily no more
.I opens
can be accepted.
.en 24 EMFILE "Too many open files
The limit on the number of open files per process, OPEN_MAX, is reached.
As released, this limit is 20 for MINIX 3, and 30 for Minix-vmd.
.en 25 ENOTTY "Not a typewriter
The file mentioned in an
.B ioctl
is not a terminal or one of the
devices to which this call applies. (Often seen error from programs with
bugs in their error reporting code.)
.It Er 19 ENODEV Em "Operation not supported by device" .
An attempt was made to apply an inappropriate
function to a device,
for example,
trying to read a write-only device such as a printer.
.It Er 20 ENOTDIR Em "Not a directory" .
A component of the specified pathname existed, but it was
not a directory, when a directory was expected.
.It Er 21 EISDIR Em "Is a directory" .
An attempt was made to open a directory with write mode specified.
.It Er 22 EINVAL Em "Invalid argument" .
Some invalid argument was supplied.
(For example, specifying an undefined signal to a
.Xr signal 3
or
.Xr kill 2
function).
.It Er 23 ENFILE Em "Too many open files in system" .
Maximum number of file descriptors allowable on the system
has been reached and a requests for an open cannot be satisfied
until at least one has been closed.
.It Er 24 EMFILE Em "Too many open files" .
\*[Lt]As released, the limit on the number of
open files per process is 64.\*[Gt]
The
.Xr getrlimit 2
call with the
.Ar RLIMIT_NOFILE
resource will obtain the current limit.
.It Er 25 ENOTTY Em "Inappropriate ioctl for device" .
A control function (see
.Xr ioctl 2 )
was attempted for a file or
special device for which the operation was inappropriate.
.en 26 ETXTBSY "Text file busy
Attempt to execute a program that is open for writing. Obsolete under MINIX 3.
.en 27 EFBIG "File too large
The size of a file exceeded the maximum (little over 64 megabytes for
the V2 file system).
.en 28 ENOSPC "No space left on device
.It Er 27 EFBIG Em "File too large" .
The size of a file exceeded the maximum.
(The system-wide maximum file size is
2147483648 (2GB) bytes.
Each file system may impose a lower limit for files contained within it).
.It Er 28 ENOSPC Em "Device out of space" .
A
.B write
.Xr write 2
to an ordinary file, the creation of a
directory or symbolic link, or the creation of a directory
entry failed because no more disk blocks are available
entry failed because no more disk blocks were available
on the file system, or the allocation of an inode for a newly
created file failed because no more inodes are available
created file failed because no more inodes were available
on the file system.
.en 29 ESPIPE "Illegal seek
.It Er 29 ESPIPE Em "Illegal seek" .
An
.B lseek
was issued to a pipe or TCP/IP channel.
This error may also be issued for
other non-seekable devices.
.en 30 EROFS "Read-only file system
An attempt to modify a file or directory
.Xr lseek 2
function was issued on a socket, pipe or
.Tn FIFO .
.It Er 30 EROFS Em "Read-only file system" .
An attempt was made to modify a file or directory
was made
on a device mounted read-only.
.en 31 EMLINK "Too many links
An attempt to make more than a certain number of hard links to a file. The
advertized maximum, LINK_MAX, is 127, but Minix-vmd uses a much larger
maximum of 32767 for the V2 file system.
.en 32 EPIPE "Broken pipe
A write on a pipe or TCP/IP channel for which there is no process
on a file system that was read-only at the time.
.It Er 31 EMLINK Em "Too many links" .
The number of hard links to a single file has exceeded the maximum.
(The system-wide maximum number of hard links is 32767.
Each file system may impose a lower limit for files contained within it).
.It Er 32 EPIPE Em "Broken pipe" .
A write on a pipe, socket or
.Tn FIFO
for which there is no process
to read the data.
This condition normally generates the signal SIGPIPE;
the error is returned if the signal is caught or ignored.
.en 33 EDOM "Math argument
The argument of a function in the math package
is out of the domain of the function.
.en 34 ERANGE "Result too large
The value of a function in the math package
is unrepresentable within machine precision.
.en 35 EDEADLK "Resource deadlock avoided
A process attempts to place a blocking lock on a file that is already
locked by another process and that process is waiting for the first
process to unlock a file that first process already has a lock on.
(The classic "lock A, lock B" by process 1, and "lock B, lock A" by
process 2.)
.en 36 ENAMETOOLONG "File name too long"
The path name exceeds PATH_MAX characters. PATH_MAX equals 255 as
distributed.
.en 37 ENOLCK "No locks available
The system's table of active locks is full.
.en 38 ENOSYS "Function not implemented
The system call is not supported. Either an old program uses an obsolete
call, or a program for a more capable system is run on a less capable
.It Er 33 EDOM Em "Numerical argument out of domain" .
A numerical input argument was outside the defined domain of the mathematical
function.
.It Er 34 ERANGE Em "Result too large or too small" .
The result of the function is too large or too small to be represented
in the available space.
.It Er 35 EDEADLK Em "Resource deadlock avoided" .
An attempt was made to lock a system resource that
would have resulted in a deadlock situation.
.It Er 36 ENAMETOOLONG Em "File name too long" .
A component of a path name exceeded
.Pq Dv NAME_MAX
characters, or an entire
path name exceeded 255
.Pq Dv PATH_MAX
characters.
.It Er 37 ENOLCK Em "No locks available" .
A system-imposed limit on the number of simultaneous file
locks was reached.
.It Er 38 ENOSYS Em "Function not implemented" .
Attempted a system call that is not available on this
system.
.en 39 ENOTEMPTY "Directory not empty"
A directory with entries other than \*(lq.\*(rq and \*(lq..\*(rq
.It Er 39 ENOTEMPTY Em "Directory not empty" .
A directory with entries other than
.Ql \&.
and
.Ql \&..
was supplied to a remove directory or rename call.
.en 40 ELOOP "Too many symbolic links"
A path name lookup involved too many symbolic links.
.en 41 ERESTART "Service restarted
.en 43 EIDRM "Identifier removed
.en 44 EILSEQ "Illegal byte sequence
.en 45 EFTYPE "Wrong file format or type
.en 50 EPACKSIZE "Invalid packet size
.en 51 ENOBUFS "Not enough buffers left
.en 52 EBADIOCTL "Illegal ioctl for device
.en 53 EBADMODE "Bad mode in ioctl
.en 54 EWOULDBLOCK "Would block
.en 55 ENETUNREACH "Network unreachable
.en 56 EHOSTUNREACH "Host unreachable
.en 57 EISCONN "Already connected
.en 58 EADDRINUSE "Address in use
.en 59 ECONNREFUSED "Connection refused
.en 60 ECONNRESET "Connection reset
.en 61 ETIMEDOUT "Connection timed out
.en 62 EURG "Urgent data present
.en 63 ENOURG "No urgent data present
.en 64 ENOTCONN "No connection
.en 65 ESHUTDOWN "Already shutdown
.en 66 ENOCONN "No such connection
.en 67 EAFNOSUPPORT "Address family not supported
.en 68 EPROTONOSUPPORT "Protocol not supported by AF
.en 69 EPROTOTYPE "Protocol wrong type for socket
.en 70 EINPROGRESS "Operation now in progress
.en 71 EADDRNOTAVAIL "Can't assign requested address
.en 72 EALREADY "Operation already in progress
.en 73 EMSGSIZE "Message too long
.en 74 ENOTSOCK "Socket operation on non-socket
.en 75 ENOPROTOOPT "Protocol not available
.en 76 EOPNOTSUPP "Operation not supported (has alias ENOTSUP)
.en 77 ENETDOWN "Network is down
.ig
.en XXX EDQUOT "Disc quota exceeded"
A
.B 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.
.en XXX ESTALE "Stale NFS file handle"
A client referenced a an open file, when the file has been deleted.
.en XXX EREMOTE "Too many levels of remote in path"
An attempt was made to remotely mount a file system into a path which
already has a remotely mounted component.
..
.SH DEFINITIONS
.TP 5
Process ID
.br
.It Er 40 ELOOP Em "Too many levels of symbolic links" .
A path name lookup involved more than 16
.Pq Dv SYMLOOP_MAX
symbolic links.
.It Er 41 ERESTART Em "Service restarted" .
.It Er 43 ERESTART Em "Identifier removed" .
An IPC identifier was removed while the current process was waiting on it.
.It Er 44 EILSEQ Em "Illegal byte sequence" .
A wide character/multibyte character encoding error occurred.
.It Er 45 EFTYPE Em "Inappropriate file type or format" .
Attempted a file operation on a file of a type for which it was invalid.
.It Er 50 EPACKSIZE Em "Invalid packet size" .
.It Er 51 ENOBUFS Em "\&No buffer space available" .
An operation on a socket or pipe was not performed because
the system lacked sufficient buffer space or because a queue was full.
.It Er 52 EBADIOCTL Em "Illegal ioctl for device" .
.It Er 53 EBADMODE Em "Bad mode in ioctl" .
.It Er 54 EWOULDBLOCK Em "Would block" .
.It Er 55 ENETUNREACH Em "Network is unreachable" .
A socket operation was attempted to an unreachable network.
.It Er 56 EHOSTUNREACH Em "No route to host" .
A socket operation was attempted to an unreachable host.
.It Er 57 EISCONN Em "Socket is already connected" .
A
.Xr connect 2
request was made on an already connected socket; or,
a
.Xr sendto 2
or
.Xr sendmsg 2
request on a connected socket specified a destination
when already connected.
.It Er 58 EADDRINUSE Em "Address already in use" .
Only one usage of each address is normally permitted.
.It Er 59 ECONNREFUSED Em "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 foreign host.
.It Er 60 ECONNRESET Em "Connection reset by peer" .
A connection was forcibly closed by a peer.
This normally results from a loss of the connection on the remote
socket due to a timeout or a reboot.
.It Er 61 ETIMEDOUT Em "Operation timed out" .
A
.Xr connect 2
or
.Xr send 2
request failed because the connected party did not
properly respond after a period of time.
(The timeout period is dependent on the communication protocol).
.It Er 62 EURG Em "Urgent data present" .
.It Er 63 ENOURG Em "No urgent data present" .
.It Er 64 ENOTCONN Em "Socket is not connected" .
An request to send or receive data was disallowed because
the socket was not connected and (when sending on a datagram socket)
no address was supplied.
.It Er 65 ESHUTDOWN Em "Cannot send after socket shutdown" .
A request to send data was disallowed because the socket
had already been shut down with a previous
.Xr shutdown 2
call.
.It Er 66 ENOCONN Em "No such connection" .
.It Er 67 EAFNOSUPPORT Em "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
.Tn NS
addresses with
.Tn ARPA
Internet protocols.
.It Er 68 EPROTONOSUPPORT Em "Protocol not supported" .
The protocol has not been configured into the
system or no implementation for it exists.
.It Er 69 EPROTOTYPE Em "Protocol wrong type for socket" .
A protocol was specified that does not support the semantics of the
socket type requested.
For example, you cannot use the
.Tn ARPA
Internet
.Tn UDP
protocol with type
.Dv SOCK_STREAM .
.It Er 70 EINPROGRESS Em "Operation now in progress" .
An operation that takes a long time to complete (such as
a
.Xr connect 2 )
was attempted on a non-blocking object (see
.Xr fcntl 2 ) .
.It Er 71 EADDRNOTAVAIL Em "Cannot assign requested address" .
Normally results from an attempt to create a socket with an
address not on this machine.
.It Er 72 EALREADY Em "Operation already in progress" .
An operation was attempted on a non-blocking object that already
had an operation in progress.
.It Er 73 EMSGSIZE Em "Message too long" .
A message sent on a socket was larger than the internal message buffer
or some other network limit.
.It Er 74 ENOTSOCK Em "Socket operation on non-socket" .
Self-explanatory.
.It Er 75 ENOPROTOOPT Em "Protocol option not available" .
A bad option or level was specified in a
.Xr getsockopt 2
or
.Xr setsockopt 2
call.
.It Er 76 EOPNOTSUPP Em "Operation not supported" (has alias ENOTSUP) .
The attempted operation is not supported for the type of object referenced.
Usually this occurs when a file descriptor refers to a file or socket
that cannot support this operation,
for example, trying to
.Em accept
a connection on a datagram socket.
.It Er 77 ENETDOWN Em "Network is down" .
A socket operation encountered a dead network.
.El
.Sh DEFINITIONS
.Bl -tag -width Ds
.It Process ID
Each active process in the system is uniquely identified by a positive
integer called a process ID. The range of this ID is from 1 to 29999.
The special process with process ID 1 is
.BR init ,
the ancestor of all processes.
.TP 5
Parent process ID
.br
.It Parent process ID
A new process is created by a currently active process; (see
.BR fork (2)).
The parent process ID of a process is the process ID of its creator,
unless the creator dies, then
.B init
becomes the parent of the orphaned process.
.TP 5
Process Group ID
.br
.Xr fork 2 ) .
The parent process ID of a process is initially the process ID of its creator.
If the creating process exits,
the parent process ID of each child is set to the ID of
.Em init ,
.Xr init 8 .
.It Process Group
Each active process is a member of a process group that is identified by
a positive integer called the process group ID. This is the process
ID of the group leader. This grouping permits the signaling of related
processes (see
.BR kill (2)).
.TP 5
Real User ID and Real Group ID
.br
a positive integer called the process group ID.
This is the process ID of the group leader.
This grouping permits the signaling of related processes (see
.Xr termios 4 ).
.It Session
A session is a set of one or more process groups.
A session is created by a successful call to
.Xr setsid 2 ,
which causes the caller to become the only member of the only process
group in the new session.
.It Session leader
A process that has created a new session by a successful call to
.Xr setsid 2 ,
is known as a session leader.
Only a session leader may acquire a terminal as its controlling terminal (see
.Xr termios 4 ) .
.It Controlling process
A session leader with a controlling terminal is a controlling process.
.It Controlling terminal
A terminal that is associated with a session is known as the controlling
terminal for that session and its members.
.It "Real User ID and Real Group ID"
Each user on the system is identified by a positive integer
termed the real user ID.
.IP
.Pp
Each user is also a member of one or more groups.
One of these groups is distinguished from others and
used in implementing accounting facilities. The positive
integer corresponding to this distinguished group is termed
the real group ID.
(Under standard MINIX 3 this is the only group a process can be a member of.)
.IP
used in implementing accounting facilities.
The positive integer corresponding to this distinguished group is
termed the real group ID.
.Pp
All processes have a real user ID and real group ID.
These are initialized from the equivalent attributes
of the process that created it.
.TP 5
Effective User Id, Effective Group Id, and Access Groups
.br
Access to system resources is governed by three values:
the effective user ID, the effective group ID, and the
group access list.
.IP
.It "Effective User Id, Effective Group Id, and Group Access List"
Access to system resources is governed by two values:
the effective user ID and the group access list.
(In POSIX.1, the group access list is known as the set of supplementary
group IDs, and it is unspecified whether the effective group ID is
a member of the list.)
.Pp
The effective user ID and effective group ID are initially the
process's real user ID and real group ID respectively. Either
may be modified through execution of a set-user-ID or set-group-ID
file (possibly by one its ancestors) (see
.BR execve (2)).
.IP
.Pp
The group access list is an additional set of group ID's
used only in determining resource accessibility. Access checks
are performed as described below in ``File Access Permissions''.
The maximum number of additional group ID's is NGROUPS_MAX.
For MINIX 3 this is 0, but Minix-vmd supports a list of up to 16
additional group ID's. (Also known as ``supplemental'' group ID's.)
.TP 5
Super-user
.br
used only in determining resource accessibility.
Access checks are performed as described below in
.Qq File Access Permissions .
It Super-user
A process is recognized as a
.I super-user
.Em super-user
process and is granted special privileges if its effective user ID is 0.
.TP 5
Descriptor
.br
An integer assigned by the system when a file or device is referenced
.It Descriptor
An integer assigned by the system when a file is referenced
by
.BR open (2),
.BR dup (2)
.Xr open 2
or
.BR fcntl (2)
which uniquely identifies an access path to that file or device from
.Xr dup 2 ,
or when a socket is created by
.Xr pipe 2 ,
.Xr socket 2 ,
or
.Xr socketpair 2 ,
which uniquely identifies an access path to that file or socket from
a given process or any of its children.
.TP 5
File Descriptor
Older, and often used name for a descriptor.
.TP 5
File Name
.br
Names consisting of up to NAME_MAX characters may be used to name
an ordinary file, special file, or directory. NAME_MAX is the maximum
of the maximum file name lengths of the supported file systems.
Excess characters are ignored when too long file names are used for
files in a given file system.
The maximum file name length of the V1 and V2 file systems
is 14 characters. The Minix-vmd "flex" variants of V1 and V2 have a
60 character maximum.
.IP
The characters in a file name may assume any value representable in
eight bits excluding 0 (null) and the ASCII code for / (slash).
.IP
Note that it is generally unwise to use one of \e'"<>();~$^&*|{}[]?
as part of file names because of the special meaning attached to these
characters by the shell.
.TP 5
Path Name
.br
A path name is a null-terminated character string starting with an
optional slash (/), followed by zero or more directory names separated
.It File Name
Names consisting of up to 60
.Pq Dv NAME_MAX
characters may be used to name
an ordinary file, special file, or directory.
.Pp
These characters may be selected from the set of all
.Tn ASCII
character
excluding 0 (NUL) and the
.Tn ASCII
code for
.Ql \&/
(slash).
(The parity bit, bit 7, must be 0).
.Pp
Note that it is generally unwise to use
.Ql \&* ,
.Ql \&? ,
.Ql \&[
or
.Ql \&]
as part of
file names because of the special meaning attached to these characters
by the shell.
.It Pathname
A path name is a
.Tn NUL Ns -terminated
character string starting with an
optional slash
.Ql \&/ ,
followed by zero or more directory names separated
by slashes, optionally followed by a file name.
The total length of a path name must be less than PATH_MAX characters
(255 as distributed.)
.IP
The total length of a path name must be less than 255
.Pq Dv PATH_MAX
characters.
.Pp
If a path name begins with a slash, the path search begins at the
.I root
.Em root
directory.
Otherwise, the search begins from the current working directory.
A slash by itself names the root directory. A null pathname is
illegal, use "." to refer to the current working directory.
.TP 5
Directory
.br
A slash by itself names the root directory.
An empty string is not a valid pathname.
.It Directory
A directory is a special type of file that contains entries
that are references to other files.
Directory entries are called links. By convention, a directory
contains at least two links, . and .., referred to as
.I dot
Directory entries are called links.
By convention, a directory contains at least two links,
.Ql \&.
and
.I dot-dot
respectively. Dot refers to the directory itself and
dot-dot refers to its parent directory.
.TP 5
Root Directory and Current Working Directory
.br
.Ql \&.. ,
referred to as
.Em dot
and
.Em dot-dot
respectively.
Dot refers to the directory itself and dot-dot refers to its parent directory.
.It "Root Directory and Current Working Directory"
Each process has associated with it a concept of a root directory
and a current working directory for the purpose of resolving path
name searches. A process's root directory need not be the root
name searches.
A process's root directory need not be the root
directory of the root file system.
.TP 5
File Access Permissions
.br
.It File Access Permissions
Every file in the file system has a set of access permissions.
These permissions are used in determining whether a process
may perform a requested operation on the file (such as opening
a file for writing). Access permissions are established at the
time a file is created. They may be changed at some later time
through the
.BR chmod (2)
call.
.IP
a file for writing).
Access permissions are established at the time a file is created.
They may be changed at some later time through the
.Xr chmod 2
call.
.Pp
File access is broken down according to whether a file may be: read,
written, or executed. Directory files use the execute
permission to control if the directory may be searched.
.IP
written, or executed.
Directory files use the execute permission to control if the
directory may be searched.
.Pp
File access permissions are interpreted by the system as
they apply to three different classes of users: the owner
of the file, those users in the file's group, anyone else.
Every file has an independent set of access permissions for
each of these classes. When an access check is made, the system
decides if permission should be granted by checking the access
information applicable to the caller.
.IP
each of these classes.
When an access check is made, the system decides if permission should be
granted by checking the access information applicable to the caller.
.Pp
Read, write, and execute/search permissions on
a file are granted to a process if:
.IP
.Pp
The process's effective user ID is that of the super-user.
.IP
(Note: even the super-user cannot execute a non-executable file).
.Pp
The process's effective user ID matches the user ID of the owner
of the file and the owner permissions allow the access.
.IP
.Pp
The process's effective user ID does not match the user ID of the
owner of the file, and either the process's effective
group ID matches the group ID
of the file, or the group ID of the file is in
the process's group access list,
and the group permissions allow the access.
.IP
.Pp
Neither the effective user ID nor effective group ID
and group access list of the process
match the corresponding user ID and group ID of the file,
but the permissions for ``other users'' allow access.
.IP
.Pp
Otherwise, permission is denied.
.SH SEE ALSO
.BR intro (3),
.BR strerror (3).
.It Sockets and Address Families
A socket is an endpoint for communication between processes.
Each socket has queues for sending and receiving data.
.Pp
Sockets are typed according to their communications properties.
These properties include whether messages sent and received
at a socket require the name of the partner, whether communication
is reliable, the format used in naming message recipients, etc.
.Pp
Each instance of the system supports some
collection of socket types; consult
.Xr socket 2
for more information about the types available and
their properties.
.Pp
Each instance of the system supports some number of sets of
communications protocols.
Each protocol set supports addresses of a certain format.
An Address Family is the set of addresses for a specific group of protocols.
Each socket has an address
chosen from the address family in which the socket was created.
.El
.Sh SEE ALSO
.Xr intro 3 ,
.Xr perror 3

184
man/man3/getcontext.3
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@ -1,96 +1,136 @@
.TH GETCONTEXT 3 "Mar 2, 2010"
.SH NAME
getcontext, setcontext \- get and set current user context
.SH SYNOPSIS
.nf
.ft B
#include <ucontext.h>
int getcontext(ucontext\_t *\fIucp\fP)
int setcontext(const ucontext\_t *\fIoucp\fP)
.SH DESCRIPTION
.Dd Mar 2, 2010
.Dt GETCONTEXT 3
.Os
.Sh NAME
.Nm getcontext ,
.Nm setcontext
.Nd get and set current user context
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In ucontext.h
.Ft int
.Fn getcontext "ucontext_t *ucp"
.Ft int
.Fn setcontext "const ucontext_t *ucp"
.Sh DESCRIPTION
The
.BR makecontext (3)
.Xr makecontext 3
,
.BR swapcontext (3)
.Xr swapcontext 3
,
.BR getcontext (3)
.Xr getcontext 3
, and
.BR setcontext (3)
.Xr setcontext 3
together form a set of functions that allow user-level context switching between multiple threads of control within a process.
.PP
The \fIucontext_t\fP type is a structure that has at least the following members:
.in +4
.nf
.Pp
The
.Vt ucontext_t
type is a structure that has at least the following members:
.Bd -offset 4n -literal
typedef struct __ucontext {
ucontext_t *uc_link;
sigset_t uc_sigmask;
stack_t uc_stack;
mcontext_t uc_mcontext;
...
ucontext_t *uc_link;
sigset_t uc_sigmask;
stack_t uc_stack;
mcontext_t uc_mcontext;
...
} ucontext_t;
.Ed
.fi
.in
with \fIsigset_t\fP and \fIstack_t\fP defined in
.IR <signal.h> .
Here \fIuc_link\fP points to the context that will be resumed when the current context returns (if \fIuc_link\fP is NULL, the process exits), \fIsigset_t\fP is the set of signals blocks in this context, \fIuc_stack\fP is the stack used by this context (when the context was modified by
.BR makecontext (3)),
and \fIuc_mcontext\fP is the machine-specific representation of the saved context. The \fImcontext_t\fP type is machine-dependent and opaque.
.PP
MINIX 3 has an additional \fIuc_flags\fP member that supports the following flags:
.PP
.in +2
.nf
with
.Vt sigset_t
and
.Vt stack_t
defined in
.In signal.h .
Here
.Va uc_link
points to the context that will be resumed when the current context returns (if
.Va uc_link
is NULL, the process exits),
.Va uc_sigmask
is the set of signals blocked in this context,
.Va uc_stack
is the stack used by this context (when the context was modified by
.Xr makecontext 3 ),
and
.Va uc_mcontext
is the machine-specific representation of the saved context. The
.Vt mcontext_t
type is machine-dependent and opaque.
.Pp
MINIX 3 has an additional
.Va uc_flags
member that supports the following flags:
.Pp
.Bd -offset 4n -literal
UCF_IGNSIGM /* Current signal mask is not stored or restored */
UCF_IGNFPU /* FPU state is not stored or restored for this context */
.fi
.in
.PP
.Ed
.Pp
Not storing and restoring the signal mask and/or FPU state speeds up context switching considerably.
.PP
.Pp
The
.BR getcontext ()
function initializes the structure pointed to by \fIucp\fP to the current user context of the calling thread.
.PP
.Fn getcontext
function initializes the structure pointed to by
.Va ucp
to the current user context of the calling thread.
.Pp
The
.BR setcontext ()
function restores the user context pointed to by \fIucp\fP. A succesful call does not return; program execution resumes at the point specified by the \fIucp\fP argument passed to
.BR setcontext ().
The \fIucp\fP argument should be created either by a prior call to
.BR getcontext ()
.Fn setcontext
function restores the user context pointed to by
.Va ucp .
A succesful call does not return; program execution resumes at the point specified by the
.Va ucp
argument passed to
.Fn setcontext .
The
.Va ucp
argument should be created either by a prior call to
.Fn getcontext
or
.BR makecontext ().
If the \fIucp\fP argument was created with
.BR getcontext (),
.Fn makecontext .
If the
.Va ucp
argument was created with
.Fn getcontext ,
program execution continues as if the corresponding call of
.BR getcontext ()
had just returned. If the \fIucp\fP argument was created with
.BR makecontext (),
.Fn getcontext
had just returned. If the
.Va ucp
argument was created with
.Fn makecontext ,
program execution continues with the function passed to
.BR makecontext ().
.Fn makecontext .
.SH "RETURN VALUE"
.Sh RETURN VALUES
When successful,
.BR getcontext ()
.Fn getcontext
returns 0 and
.BR setcontext ()
.Fn setcontext
does not return. Otherwise, both return -1 and
.I errno
.Va errno
is set to indicate the error.
.SH "ERRORS"
.TP 15
[EINVAL]
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EINVAL
The context is not properly initialized.
.TP 15
[EFAULT]
\fIucp\fP is a NULL pointer.
.SH "SEE ALSO"
.BR makecontext (3).
.SH "AUTHORS"
.It Bq Er EFAULT
.Va ucp
is a NULL pointer.
.El
.Sh SEE ALSO
.Xr makecontext 3 ,
.Xr swapcontext 3
.Sh STANDARDS
The
.Fn getcontext ,
and
.Fn setcontext
functions conform to
.St -xsh5
and
.St -p1003.1-2001 .
.Sh AUTHORS
Thomas Veerman

136
man/man3/makecontext.3
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@ -1,75 +1,97 @@
.TH MAKECONTEXT 3 "Mar 2, 2010"
.SH NAME
makecontext, swapcontext \- manipulate user contexts
.SH SYNOPSIS
.nf
.ft B
#include <ucontext.h>
void makecontext(ucontext\_t *\fIucp\fP, void \fI(*func)(void)\fP, int \fIargc\fP, ...)
int swapcontext(ucontext\_t *\fIoucp\fP, const ucontext\_t *\fIucp\fP)
.SH DESCRIPTION
.Dd Mar 2, 2010
.Dt MAKECONTEXT 3
.Os
.Sh NAME
.Nm makecontext ,
.Nm swapcontext
.Nd manipulate user contexts
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In ucontext.h
.Ft void
.Fn makecontext "ucontext_t *ucp" "void (*func)(void)" "int argc" ...
.Ft int
.Fn swapcontext "ucontext_t *oucp" "const ucontext_t *ucp"
.Sh DESCRIPTION
The
.BR makecontext (3)
,
.BR swapcontext (3)
,
.BR getcontext (3)
, and
.BR setcontext (3)
.Xr makecontext 3 ,
.Xr swapcontext 3 ,
.Xr getcontext 3 ,
and
.Xr setcontext 3
together form a set of functions that allow user-level context switching between multiple threads of control within a process.
.PP
.Pp
The
.BR makecontext ()
.Fn makecontext
function modifies the user thread pointed to by
.I ucp
.Va ucp
to continue execution by invoking function
.I func
.Va func
and passing that function a number of
.I argc
.Va argc
integer arguments. The value of
.I argc
.Va argc
must match the number of integer arguments passed to
.I func
, otherwise the behavior is undefined. Context
.I ucp
.Va func ,
otherwise the behavior is undefined. Context
.Va ucp
must have been initialized by a call to
.BR getcontext (3)
and have a stack allocated for it. The address of the stack must be assigned to \fIucp\->uc_stack.ss_sp\fP and the size of the stack to \fIucp\->uc_stack.ss_size\fP. The \fIucp\->uc_link\fP member is used to determine which successor context is run after the context modified by
.BR makecontext ()
returns. If left NULL, the process exits.
.PP
.Xr getcontext 3
and have a stack allocated for it. The address of the stack must be assigned to
.Va ucp->uc_stack.ss_sp
and the size of the stack to
.Va ucp->uc_stack.ss_size .
The
.BR swapcontext ()
.Va ucp->uc_link
member is used to determine which successor context is run after the context modified by
.Fn makecontext
returns. If left NULL, the process exits.
.Pp
The
.Fn swapcontext
function saves the current context in the context structure pointed to by
.I oucp
and sets the context to the context structure pointed to by \fIucp\fP.
.SH "RETURN VALUE"
.Va oucp
and sets the context to the context structure pointed to by
.Va ucp .
.Sh RETURN VALUES
When successful,
.BR swapcontext ()
.Fn swapcontext
returns 0. Otherwise, -1 is returned and
.I errno
.Va errno
is set to indicate the error. Note that a successful call to
.BR swapcontext ()
.Fn swapcontext
actually does not return. Only after returning to the context that called
.BR swapcontext ()
, it appears as if
.BR swapcontext ()
.Fn swapcontext ,
it appears as if
.Fn swapcontext
returned 0.
.SH "ERRORS"
.TP 15
[EFAULT]
Either the \fIucp\fP or \fIoucp\fP is a NULL pointer.
.TP 15
[EINVAL]
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EFAULT
Either the
.Va ucp
or
.Va oucp
is a NULL pointer.
.It Bq Er EINVAL
The context is not properly initialized.
.TP 15
[ENOMEM]
The \fIucp\fP argument does not have enough stack left to complete the operation.
.SH "SEE ALSO"
.BR getcontext (3).
.SH "AUTHORS"
.It Bq Er ENOMEM
The
.Va ucp
argument does not have enough stack left to complete the operation.
.El
.Sh SEE ALSO
.Xr getcontext 3 ,
.Xr setcontext 3
.Sh STANDARDS
The
.Fn makecontext ,
and
.Fn swapcontext
functions conform to
.St -xsh5
and
.St -p1003.1-2001 .
.Sh AUTHORS
Thomas Veerman