.TH INTRO 2 .de en .HP \\$1 \\fL\\$2\\fP \\$3 .br .. .SH NAME intro, errno \(mi introduction to system calls and error numbers .SH SYNOPSIS .B #include .SH DESCRIPTION Section 2 describes the entries into the kernel. .PP Calls that deal with file systems refer to directory entries by name. In order to .I read or .IR write (2) data on a file, the file must be opened .RI ( open, .I pipe, .IR creat (2)); an open file is known by a integer called a .IR "file descriptor" . Certain open files admit control operations that alter their behavior; see in particular .IR ioctl (2), .IR stream (4), and .IR ttyld (4). .PP Besides ordinary file systems, which are passive repositories of data, organized in a hierarchical directory structure, there are special file systems \(em virtual constructs with an interface that mimics an ordinary file system. In particular, access to files on remote computers is mediated by the special file system .IR netfs (8). Other special file systems support .IR proc (4) and .IR faced (9.5). .SH SEE ALSO .IR intro (3) .SH DIAGNOSTICS A `Diagnostics' paragraph appears below for each system call that has an error return. Unless otherwise stated, the error value is the integer \-1, and the success value is 0. Upon an error return, an error number is assigned to the external variable .IR errno . .I Errno is not cleared on successful calls, so it should be tested only after an error has occurred. .PP There is a table of messages that describe the errors and a routine for printing them; see .IR perror (3). The list below gives the number, the name (as defined in .BR ), and the .I perror message for each error type. The reasons for error returns are explained in general terms; further explanations for less obvious error returns appear in the writeups of individual system calls. .en 0 \h'\w'EIO'u' "Error 0 No error has occurred. .en 1 EPERM "Not owner An attempt was made to modify a file in some way forbidden except to its owner or the super-user, or an ordinary user attempted to do something allowed only to the super-user. .en 2 ENOENT "No such file or directory A file name was specified and the file should exist but doesn't, or one of the directories in a path name does not exist. .en 3 ESRCH "No such process The process whose number was given to .I kill does not exist, or is already dead. .en 4 EINTR "Interrupted system call An asynchronous signal (such as interrupt or quit), which the user has elected to catch, occurred during a system call. If execution is resumed after processing the signal, it will appear as if the interrupted system call returned this error condition. .en 5 EIO "I/O error A physical I/O error or timeout occurred during .IR read , .I write, or .I ioctl. This error may in some cases be returned on a call following the one to which it actually applies. .en 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 off line or no disk pack is loaded on a drive. .en 7 E2BIG "Arg list too long An argument list longer than 16384 bytes was presented to .IR exec . .en 8 ENOEXEC "Exec format error A request was made to execute a file which, although it has the appropriate permissions, does not start with a valid magic number, see .IR a.out (5). .en 9 EBADF "Bad file number A file descriptor referred to no open file, or a read (resp. write) request was made to a file which is open only for writing (resp. reading). .en 10 ECHILD "No children In a .IR wait , the process had no living or unwaited-for children. .en 11 EAGAIN "No more processes In a .IR fork , the system's process table was full or the user is not allowed to create any more processes. .en 12 ENOMEM "Not enough memory During an .I exec or .I brk, a program asked for more memory or swap space than the system is able to supply. .en 13 EACCES "Permission denied An attempt was made to access a file in a way forbidden by the protection system. .en 14 EFAULT "Bad address The system encountered a hardware fault in attempting to access the arguments of a system call. .en 15 EHASF "Directory not empty An attempt was made to remove a nonempty directory. .en 16 EBUSY "In use An attempt was made to mount a device that was already mounted (or crashed or was copied in mounted state), to dismount a device on which there is an active file (open file, current directory, mounted-on file, active text segment), or to remove the current directory of some process. .en 17 EEXIST "File exists An existing file was mentioned in an inappropriate context, e.g. .IR link . .en 18 EXDEV "Cross-device link A link to a file on another device was attempted. .en 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. .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 .IR 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 .IR signal , reading or writing a file for which .I lseek has generated a negative pointer. Also set by math functions, see .IR intro (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 is 128 per process. .en 25 ENOTTY "Illegal ioctl The function code mentioned in .I ioctl does not apply to the file or device. .en 26 ETXTBSY "Text file busy An attempt to execute a pure-procedure program which is currently open. Also an attempt to open for writing a pure-procedure program that is being executed. .en 27 EFBIG "File too large The size of a file exceeded the maximum (about .if t 10\u\s-29\s+2\d .if n 1.0E9 bytes). .en 28 ENOSPC "No space left on device During a .I write to an ordinary file, there was no free space left on the device. .en 29 ESPIPE "Illegal seek An .I lseek was issued to a pipe or other non-seekable device. .en 30 EROFS "Read-only file system An attempt 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 32767 links to a file. .en 32 EPIPE "Broken pipe A write on a pipe for which there is no process to read the data, or on a file with insufficient security clearance. This condition normally generates a signal; the error is returned if the signal is ignored. .en 33 EDOM "Math argument The argument of a function in the math package (3M) is out of the domain of the function. .en 34 ERANGE "Result too large The value of a function in the math package (3M) is unrepresentable within machine precision. .en 35 ELOOP "Link loop An endless cycle of symbolic links was encountered. .en 36 ECONC "Concurrency violation The open was in violation of the concurrent access specified for the file, or an attempted IO operation violated a process exclusive (pex) lock. .en 37 EGREG "It's all Greg's fault Something went wrong. .en 38 ELAB "Security label violation An action which would, if completed, break security rules; see .IR getplab (2). .en 39 ENOSYS "No such system call An attempt to execute a nonexistent or unsupported system call. .en 40 ENLAB "Out of security labels A system table for security labels is full: a trouble similar to .BR ENFILE . .en 41 EPRIV "Insufficient privilege An attempt was made to execute a priviledged system call, or exercise a privileged feature of a regular system call. .SH SEE ALSO .IR perror (3) .SH BUGS Device drivers and special file systems may use error codes in unexpected or unconventional ways; it is infeasible to list them all. For example, the crash of a remote computer or the failure of a communication protocol can produce .L ENOENT (no such file or directory) in response to an attempt to open a file through the network file system. .br To avoid publishing duplicates of trivially changed manual pages, .L ELAB is not recorded among diagnostics when that would be the only difference from v9.