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diff --git a/lib/libc/sys/intro.2 b/lib/libc/sys/intro.2 deleted file mode 100644 index 1b84b219fe0e..000000000000 --- a/lib/libc/sys/intro.2 +++ /dev/null @@ -1,767 +0,0 @@ -.\" Copyright (c) 1980, 1983, 1986, 1991, 1993 -.\" The Regents of the University of California. All rights reserved. -.\" -.\" Redistribution and use in source and binary forms, with or without -.\" modification, are permitted provided that the following conditions -.\" are met: -.\" 1. Redistributions of source code must retain the above copyright -.\" notice, this list of conditions and the following disclaimer. -.\" 2. Redistributions in binary form must reproduce the above copyright -.\" notice, this list of conditions and the following disclaimer in the -.\" documentation and/or other materials provided with the distribution. -.\" 3. Neither the name of the University nor the names of its contributors -.\" may be used to endorse or promote products derived from this software -.\" without specific prior written permission. -.\" -.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND -.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE -.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE -.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE -.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL -.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS -.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) -.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT -.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY -.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF -.\" SUCH DAMAGE. -.\" -.\" @(#)intro.2 8.5 (Berkeley) 2/27/95 -.\" -.Dd September 8, 2016 -.Dt INTRO 2 -.Os -.Sh NAME -.Nm intro -.Nd introduction to system calls and error numbers -.Sh LIBRARY -.Lb libc -.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. -.\".Pp -.\".Sy System call restart -.\".Pp -.\"(more later...) -.Sh RETURN VALUES -Nearly all of the system calls provide an error number referenced via -the external identifier errno. -This identifier is defined in -.In sys/errno.h -as -.Pp -.Dl extern int * __error(); -.Dl #define errno (* __error()) -.Pp -The -.Va __error() -function returns a pointer to a field in the thread specific structure for -threads other than the initial thread. -For the initial thread and -non-threaded processes, -.Va __error() -returns a pointer to a global -.Va errno -variable that is compatible with the previous definition. -.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. -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 -The following is a complete list of the errors and their -names as given in -.In sys/errno.h . -.Bl -hang -width Ds -.It Er 0 Em "Undefined error: 0" . -Not used. -.It Er 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 system call" . -An asynchronous signal (such as -.Dv SIGINT -or -.Dv SIGQUIT ) -was caught by the process during the execution of an interruptible -function. -If the signal handler performs a normal return, the -interrupted system 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 "Argument list too long" . -The number of bytes used for the argument and environment -list of the new process exceeded the current limit -.Dv ( NCARGS -in -.In sys/param.h ) . -.It Er 8 ENOEXEC Em "Exec format error" . -A request was made to execute a file -that, although it has the appropriate permissions, -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 read (write) request was made to a file that was only open for -writing (reading). -.It Er 10 ECHILD Em "\&No child processes" . -A -.Xr wait 2 -or -.Xr waitpid 2 -function was executed by a process that had no existing or unwaited-for -child processes. -.It Er 11 EDEADLK Em "Resource deadlock avoided" . -An attempt was made to lock a system resource that -would have resulted in a deadlock situation. -.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. -A lack of swap space is normally temporary; however, -a lack of core is not. -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 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. -.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 "Device 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, -for instance, as the new link name in a -.Xr link 2 -system call. -.It Er 18 EXDEV Em "Cross-device link" . -A hard link to a file on another file system -was attempted. -.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 -function -or a -.Xr kill 2 -system call). -.It Er 23 ENFILE Em "Too many open files in system" . -Maximum number of open files allowable on the system -has been reached and requests for an open cannot be satisfied -until at least one has been closed. -.It Er 24 EMFILE Em "Too many open files" . -Maximum number of file descriptors allowable in the process -has been reached and requests for an open cannot be satisfied -until at least one has been closed. -The -.Xr getdtablesize 2 -system call 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. -.It Er 26 ETXTBSY Em "Text file busy" . -The new process was a pure procedure (shared text) file -which was open for writing by another process, or -while the pure procedure file was being executed an -.Xr open 2 -call requested write access. -.It Er 27 EFBIG Em "File too large" . -The size of a file exceeded the maximum. -.It Er 28 ENOSPC Em "No space left on device" . -A -.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 were available -on the file system, or the allocation of an inode for a newly -created file failed because no more inodes were available -on the file system. -.It Er 29 ESPIPE Em "Illegal seek" . -An -.Xr lseek 2 -system call 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 -on a file system that was read-only at the time. -.It Er 31 EMLINK Em "Too many links" . -Maximum allowable hard links to a single file has been exceeded (limit -of 32767 hard links per file). -.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. -.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" . -A numerical result of the function was too large to fit in the -available space (perhaps exceeded precision). -.It Er 35 EAGAIN Em "Resource temporarily unavailable" . -This is a temporary condition and later calls to the -same routine may complete normally. -.It Er 36 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 37 EALREADY Em "Operation already in progress" . -An operation was attempted on a non-blocking object that already -had an operation in progress. -.It Er 38 ENOTSOCK Em "Socket operation on non-socket" . -Self-explanatory. -.It Er 39 EDESTADDRREQ Em "Destination address required" . -A required address was omitted from an operation on a socket. -.It Er 40 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 41 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 42 ENOPROTOOPT Em "Protocol not available" . -A bad option or level was specified in a -.Xr getsockopt 2 -or -.Xr setsockopt 2 -call. -.It Er 43 EPROTONOSUPPORT Em "Protocol not supported" . -The protocol has not been configured into the -system or no implementation for it exists. -.It Er 44 ESOCKTNOSUPPORT Em "Socket type not supported" . -The support for the socket type has not been configured into the -system or no implementation for it exists. -.It Er 45 EOPNOTSUPP Em "Operation not supported" . -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 46 EPFNOSUPPORT Em "Protocol family not supported" . -The protocol family has not been configured into the -system or no implementation for it exists. -.It Er 47 EAFNOSUPPORT Em "Address family not supported by protocol family" . -An address incompatible with the requested protocol was used. -For example, you should not necessarily expect to be able to use -.Tn NS -addresses with -.Tn ARPA -Internet protocols. -.It Er 48 EADDRINUSE Em "Address already in use" . -Only one usage of each address is normally permitted. -.It Er 49 EADDRNOTAVAIL Em "Can't assign requested address" . -Normally results from an attempt to create a socket with an -address not on this machine. -.It Er 50 ENETDOWN Em "Network is down" . -A socket operation encountered a dead network. -.It Er 51 ENETUNREACH Em "Network is unreachable" . -A socket operation was attempted to an unreachable network. -.It Er 52 ENETRESET Em "Network dropped connection on reset" . -The host you were connected to crashed and rebooted. -.It Er 53 ECONNABORTED Em "Software caused connection abort" . -A connection abort was caused internal to your host machine. -.It Er 54 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 55 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 56 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 57 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 58 ESHUTDOWN Em "Can't 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 60 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 61 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 62 ELOOP Em "Too many levels of symbolic links" . -A path name lookup involved more than 32 -.Pq Dv MAXSYMLINKS -symbolic links. -.It Er 63 ENAMETOOLONG Em "File name too long" . -A component of a path name exceeded -.Brq Dv NAME_MAX -characters, or an entire -path name exceeded -.Brq Dv PATH_MAX -characters. -(See also the description of -.Dv _PC_NO_TRUNC -in -.Xr pathconf 2 . ) -.It Er 64 EHOSTDOWN Em "Host is down" . -A socket operation failed because the destination host was down. -.It Er 65 EHOSTUNREACH Em "No route to host" . -A socket operation was attempted to an unreachable host. -.It Er 66 ENOTEMPTY Em "Directory not empty" . -A directory with entries other than -.Ql .\& -and -.Ql ..\& -was supplied to a remove directory or rename call. -.It Er 67 EPROCLIM Em "Too many processes" . -.It Er 68 EUSERS Em "Too many users" . -The quota system ran out of table entries. -.It Er 69 EDQUOT Em "Disc quota exceeded" . -A -.Xr write 2 -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. -.It Er 70 ESTALE Em "Stale NFS file handle" . -An attempt was made to access an open file (on an -.Tn NFS -file system) -which is now unavailable as referenced by the file descriptor. -This may indicate the file was deleted on the -.Tn NFS -server or some -other catastrophic event occurred. -.It Er 72 EBADRPC Em "RPC struct is bad" . -Exchange of -.Tn RPC -information was unsuccessful. -.It Er 73 ERPCMISMATCH Em "RPC version wrong" . -The version of -.Tn RPC -on the remote peer is not compatible with -the local version. -.It Er 74 EPROGUNAVAIL Em "RPC prog. not avail" . -The requested program is not registered on the remote host. -.It Er 75 EPROGMISMATCH Em "Program version wrong" . -The requested version of the program is not available -on the remote host -.Pq Tn RPC . -.It Er 76 EPROCUNAVAIL Em "Bad procedure for program" . -An -.Tn RPC -call was attempted for a procedure which does not exist -in the remote program. -.It Er 77 ENOLCK Em "No locks available" . -A system-imposed limit on the number of simultaneous file -locks was reached. -.It Er 78 ENOSYS Em "Function not implemented" . -Attempted a system call that is not available on this -system. -.It Er 79 EFTYPE Em "Inappropriate file type or format" . -The file was the wrong type for the operation, or a data file had -the wrong format. -.It Er 80 EAUTH Em "Authentication error" . -Attempted to use an invalid authentication ticket to mount a -.Tn NFS -file system. -.It Er 81 ENEEDAUTH Em "Need authenticator" . -An authentication ticket must be obtained before the given -.Tn NFS -file system may be mounted. -.It Er 82 EIDRM Em "Identifier removed" . -An IPC identifier was removed while the current process was waiting on it. -.It Er 83 ENOMSG Em "No message of desired type" . -An IPC message queue does not contain a message of the desired type, or a -message catalog does not contain the requested message. -.It Er 84 EOVERFLOW Em "Value too large to be stored in data type" . -A numerical result of the function was too large to be stored in the caller -provided space. -.It Er 85 ECANCELED Em "Operation canceled" . -The scheduled operation was canceled. -.It Er 86 EILSEQ Em "Illegal byte sequence" . -While decoding a multibyte character the function came along an -invalid or an incomplete sequence of bytes or the given wide -character is invalid. -.It Er 87 ENOATTR Em "Attribute not found" . -The specified extended attribute does not exist. -.It Er 88 EDOOFUS Em "Programming error" . -A function or API is being abused in a way which could only be detected -at run-time. -.It Er 89 EBADMSG Em "Bad message" . -A corrupted message was detected. -.It Er 90 EMULTIHOP Em "Multihop attempted" . -This error code is unused, but present for compatibility with other systems. -.It Er 91 ENOLINK Em "Link has been severed" . -This error code is unused, but present for compatibility with other systems. -.It Er 92 EPROTO Em "Protocol error" . -A device or socket encountered an unrecoverable protocol error. -.It Er 93 ENOTCAPABLE Em "Capabilities insufficient" . -An operation on a capability file descriptor requires greater privilege than -the capability allows. -.It Er 94 ECAPMODE Em "Not permitted in capability mode" . -The system call or operation is not permitted for capability mode processes. -.It Er 95 ENOTRECOVERABLE Em "State not recoverable" . -The state protected by a robust mutex is not recoverable. -.It Er 96 EOWNERDEAD Em "Previous owner died" . -The owner of a robust mutex terminated while holding the mutex lock. -.It Er 97 EINTEGRITY Em "Integrity check failed" . -An integrity check such as a check-hash or a cross-correlation failed. -The integrity error falls in the kernel I/O stack between -.Er EINVAL -that identifies errors in parameters to a system call and -.Er EIO -that identifies errors with the underlying storage media. -It is typically raised by intermediate kernel layers such as a -filesystem or an in-kernel GEOM subsystem when they detect inconsistencies. -Uses include allowing the -.Xr mount 8 -command to return a different exit value to automate the running of -.Xr fsck 8 -during a system boot. -.El -.Sh DEFINITIONS -.Bl -tag -width Ds -.It Process ID . -Each active process in the system is uniquely identified by a non-negative -integer called a process ID. -The range of this ID is from 0 to 99999. -.It Parent process ID -A new process is created by a currently active process (see -.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 the calling process's -reaper (see -.Xr procctl 2 ) , -normally -.Xr init 8 . -.It Process Group -Each active process is a member of a process group that is identified by -a non-negative 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 ) -and the job control mechanisms of -.Xr csh 1 . -.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 "Terminal Process Group ID" -A terminal may be acquired by a session leader as its controlling terminal. -Once a terminal is associated with a session, any of the process groups -within the session may be placed into the foreground by setting -the terminal process group ID to the ID of the process group. -This facility is used -to arbitrate between multiple jobs contending for the same terminal; -(see -.Xr csh 1 -and -.Xr tty 4 ) . -.It "Orphaned Process Group" -A process group is considered to be -.Em orphaned -if it is not under the control of a job control shell. -More precisely, a process group is orphaned -when none of its members has a parent process that is in the same session -as the group, -but is in a different process group. -Note that when a process exits, the parent process for its children -is normally changed to be -.Xr init 8 , -which is in a separate session. -Not all members of an orphaned process group are necessarily orphaned -processes (those whose creating process has exited). -The process group of a session leader is orphaned by definition. -.It "Real User ID and Real Group ID" -Each user on the system is identified by a positive integer -termed the real user ID. -.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. -.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. -.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. -The first member of the group access list is also known as the -effective group ID. -(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 -.Xr execve 2 ) . -By convention, the effective group ID (the first member of the group access -list) is duplicated, so that the execution of a set-group-ID program -does not result in the loss of the original (real) group ID. -.Pp -The group access list is a set of group IDs -used only in determining resource accessibility. -Access checks -are performed as described below in ``File Access Permissions''. -.It "Saved Set User ID and Saved Set Group ID" -When a process executes a new file, the effective user ID is set -to the owner of the file if the file is set-user-ID, and the effective -group ID (first element of the group access list) is set to the group -of the file if the file is set-group-ID. -The effective user ID of the process is then recorded as the saved set-user-ID, -and the effective group ID of the process is recorded as the saved set-group-ID. -These values may be used to regain those values as the effective user -or group ID after reverting to the real ID (see -.Xr setuid 2 ) . -(In POSIX.1, the saved set-user-ID and saved set-group-ID are optional, -and are used in setuid and setgid, but this does not work as desired -for the super-user.) -.It Super-user -A process is recognized as a -.Em super-user -process and is granted special privileges if its effective user ID is 0. -.It Descriptor -An integer assigned by the system when a file is referenced -by -.Xr open 2 -or -.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. -.It File Name -Names consisting of up to -.Brq Dv NAME_MAX -characters may be used to name -an ordinary file, special file, or directory. -.Pp -These characters may be arbitrary eight-bit values, -excluding -.Dv NUL -.Tn ( ASCII -0) and the -.Ql \&/ -character (slash, -.Tn ASCII -47). -.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 Path Name -A path name is a -.Dv 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 -.Brq Dv PATH_MAX -characters. -(On some systems, this limit may be infinite.) -.Pp -If a path name begins with a slash, the path search begins at the -.Em root -directory. -Otherwise, the search begins from the current working directory. -A slash by itself names the root directory. -An empty -pathname refers to the current directory. -.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, -.Ql .\& -and -.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 -directory of the root file system. -.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 -.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. -.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. -.Pp -Read, write, and execute/search permissions on -a file are granted to a process if: -.Pp -The process's effective user ID is that of the super-user. -(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. -.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. -.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. -.Pp -Otherwise, permission is denied. -.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 |