INTRO(2) COMMAND REFERENCE INTRO(2) NAME intro - introduction to system calls and error numbers SYNOPSIS #include <errno.h> DESCRIPTION This section describes all 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. As with normal arguments, all return codes and values from functions are of type int unless otherwise noted. 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. The following is a complete list of the errors and their names as given in <errno.h>. Only these symbolic names for error numbers should be used in programs, since the actual value of the error number may vary with the implementation. Certain implementations may contain extensions which prevent some errors from ever occurring. 0 Unused 1 EPERM Not file owner or superuser Typically this error indicates an attempt to modify a file in some way forbidden by the file protection codes; the error is also returned for attempts by ordinary users to do things allowed only to the superuser. 2 ENOENT No such file or directory This error occurs when a file name is specified and the file should exist but doesn't, when the specified file is a symbolic link to a file or directory that does not exist, or when one of the directories in a path name does not exist. 3 ESRCH No such process No such process can be found corresponding to that specified by the process ID. 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 appears as if the interrupted system call returned this error condition. Printed 4/6/89 1
INTRO(2) COMMAND REFERENCE INTRO(2) 5 EIO I/O error Some physical I/O error occurred during a read or write; 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 the file is beyond the limits of the device. The error may also occur when, for example, a tape drive is not online, or a disk pack is not loaded on a drive. 7 E2BIG Argument list too long An argument list longer than NCARGS (defined in <sys/param.h>) bytes is presented to a member of the exec family. 8 ENOEXEC Exec format error A request is made to execute a file which, although it has the appropriate permissions, is not in the proper format for an executable object program. See a.out(5). 9 EBADF Bad file number Either a file descriptor refers to no open file, or a read (respectively write) request is made to a file which is open only for writing (respectively reading). 10 ECHILD No children from process Wait and the process has no living or unwaited-for children. 11 EAGAIN No more processes A fork failed because the system's process table is full or the user is not allowed to create any more processes. This may be a temporary condition and subsequent calls to the same routine may complete normally. 12 ENOMEM Not enough core or swap space During an execve or brk or sbrk, a program asks for more core or swap space than the system is able to supply. A lack of swap space is normally a temporary condition. However, a lack of core is not a temporary condition; the maximum core size is a system parameter. 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 access an argument of a system call. Printed 4/6/89 2
INTRO(2) COMMAND REFERENCE INTRO(2) 15 ENOTBLK Block device required A non-block file was mentioned where a block device was required, e.g. in mount. 16 EBUSY Mount device busy An attempt was made to access a device that was already in use, such as mounting a device that is already mounted. This error is also returned if an attempt is made to dismount a device on which there is an active file directory (open file, current directory, mounted- on file, active text segment). 17 EEXIST File exists An existing file was mentioned in an inappropriate context, e.g. link. 18 EXDEV Cross-device link A hard link to a file on another device was attempted. 19 ENODEV No such device driver or operation 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, for example in a path name or as an argument to chdir(2). 21 EISDIR Is a directory An attempt was made to write on a directory. 22 EINVAL Invalid argument Some invalid argument (e.g., mentioning an unknown signal in kill, reading or writing a file for which lseek has generated a negative pointer) has been used. Also set by math functions; see intro(3m). 23 ENFILE File table overflow The system's table of open files is full, and temporarily no more opens can be accepted. 24 EMFILE Too many open files No process may have more than NOFILE (defined in <sys/max.h>) file descriptors open at a time. 25 ENOTTY Request does not apply A given request is not recognized by or does not apply to a specified file or device. 26 ETXTBSY Text file busy An attempt was made to open(2) for writing a shared- text file that is being executed. Printed 4/6/89 3
INTRO(2) COMMAND REFERENCE INTRO(2) 27 EFBIG File too large The size of a file exceeded the maximum file size. 28 ENOSPC No space left on device During a write 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 on the file system, or the allocation of an inode for a newly-created file failed because no inodes are available on the file system. 29 ESPIPE Illegal seek An lseek was issued to a pipe; this error may also be issued for other non-seekable devices. 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 was made to make more than the legal limit of hard links to a file. 32 EPIPE Unconnected pipe A write on a pipe or socket was attempted, for which there is no process to read the data. This condition normally generates a signal; the error is returned if the signal is ignored. 33 EDOM Math argument out of range The argument of a function in the math package (see intro(3m)) is out of the domain of the function. 34 ERANGE Result too large The value of a function in the math package is not representable within machine precision. 35 EWOULDBLOCK Operation would block An operation which would cause a process to block was attempted on an object while in non-blocking mode (see ioctl(2)). 36 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)). 37 EALREADY Disconnection already in progress An operation was attempted on a non-blocking object which already had an operation in progress. Printed 4/6/89 4
INTRO(2) COMMAND REFERENCE INTRO(2) 38 ENOTSOCK Socket operation on non-socket Self-explanatory. 39 EDESTADDRREQ Destination address required A required address was omitted from an operation on a socket. 40 EMSGSIZE Message too long A message sent on a socket was larger than the internal message buffer. 41 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. 42 ENOPROTOOPT Protocol not available A bad option was specified in a getsockopt(2) or setsockopt(2) call. 43 EPROTONOSUPPORT Protocol not supported The protocol has not been configured into the system or no implementation for it exists. 44 ESOCKTNOSUPPORT Socket type not supported The support for the socket type has not been configured into the system or no implementation for it exists. 45 EOPNOTSUPP Operation not supported on socket For example, trying to accept a connection on a datagram socket. 46 EPFNOSUPPORT Protocol family not supported The protocol family has not been configured into the system or no implementation for it exists. 47 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. 48 EADDRINUSE Address already in use Only one usage of each address is normally permitted. 49 EADDRNOTAVAIL Can't assign requested address Normally results from an attempt to create a socket with an address not on this machine. Printed 4/6/89 5
INTRO(2) COMMAND REFERENCE INTRO(2) 50 ENETDOWN Network is down A socket operation encountered a dead network. 51 ENETUNREACH Network is unreachable A socket operation was attempted to an unreachable network. 52 ENETRESET Network dropped connection on reset The host you were connected to crashed and rebooted. 53 ECONNABORTED Software caused connection abort A connection abort was caused internal to your host machine. 54 ECONNRESET Connection reset by remote host A connection was forcibly closed by a peer; this normally results from the peer executing a shutdown(2) call. 55 ENOBUFS No buffer space available An operation on a socket or pipe was not performed because the system lacked sufficient buffer space. 56 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. 57 ENOTCONN Socket is not connected An request to send or receive data was disallowed because the socket is not connected. 58 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. 59 ETOOMANYREFS Too many references; can't splice Unused. 60 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.) 61 ECONNREFUSED Connection refused No connection could be made because the target machine actively refused it; this usually results from trying to connect to a service which is inactive on the foreign host. Printed 4/6/89 6
INTRO(2) COMMAND REFERENCE INTRO(2) 62 ELOOP Too many levels of symbolic links A path name lookup involved more than 8 symbolic links. 63 ENAMETOOLONG File name too long A component of a path name exceeded MAXNAMLEN characters, or an entire path name exceeded MAXPATHLEN characters; these are defined in <sys/max.h>. 64 EHOSTDOWN Host is down A requested host is not responding. 65 EHOSTUNREACH Host is unreachable A requested host is not reachable from the current node. 66 ENOTEMPTY Directory not empty A directory with entries other than "." and ".." was supplied to a remove directory or rename call. 67 EPROCLIM Too many processes Unused. 68 EUSERS Too many users Unused. 69 EDQUOT Disk quota exceeded Unused. 70 ENOASCII Name contains byte with high-order bit set A given path name contains a non-ASCII character, a byte with the high-order bit set. 71 EMCOLLIDE Map onto something already there New areas may only be added where there is currently no memory. If you want to replace an area, unmap it first. 72 EMRANGE Designated area out of range Possible problems: any part of the addressed area 1) crosses the P0:P1 boundary (on a VAX); 2) is in the u area; 3) is out of the user's address space. 73 EDFS_CD Too many chdir's to remote host(s) 74 EDFSREF Reference is to remote file 75 EDFSBADRESP Response length incorrect 76 EDFSBADCMD Bad command (invalid command; wrong length) 77 EDFSNOSUCHHOST Couldn't find addr of hostname Printed 4/6/89 7
INTRO(2) COMMAND REFERENCE INTRO(2) 78 EDFSNOBUF Malloc failed on remote system; try smaller ( <8K ) read or write 79 EDFSBADVER Unsupported version 80 EDFSNODAEMON DFS daemon is not running 81 EDFSNOPROC No process slots on remote system DEFINITIONS 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 0 to NPROC. Parent process ID A new process is created by a currently active process; see fork(2). The parent process ID of a process is the process ID of its creator. Process Group ID 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 killpg(2)) and the job control mechanisms of csh(1csh). Tty Group ID Each active process can be a member of a terminal group that is identified by a positive integer called the tty group ID; this grouping is used to arbitrate between multiple jobs contending for the same terminal; see csh(1csh), and tty(4). Real User ID and Real Group ID Each user allowed on the system is identified by a positive integer called a real user ID. 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. 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. Effective User ID, Effective Group ID, and Access Groups Access to system resources is governed by three values: Printed 4/6/89 8
INTRO(2) COMMAND REFERENCE INTRO(2) the effective user ID, the effective group ID, and the group access list. 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 of its ancestors); see execve(2). The group access list is an additional set of group ID's used only in determining resource accessibility. Access checks are performed as described in the section File Access Permissions. Superuser A process is recognized as a superuser process and is granted special privileges if its effective user ID is 0. Special Processes The processes with a process ID of 0, 1, and 2 are special. Process 0 is the scheduler. Process 1 is the initialization process init, and is the ancestor of every other process in the system; it controls the process structure. Process 2 is the paging daemon. Descriptor An non-negative integer assigned by the system when a file is referenced by open(2), dup(2), fcntl(2), or pipe(2), or when a socket is referenced by socket(2) or socketpair(2). The descriptor uniquely identifies an access path to that file or socket from a given process or any of its children. File Name Names consisting of up to MAXNAMLEN may be used to name an ordinary file, special file, or directory. These characters may be selected from the set of all ASCII characters excluding 0 (null) and the ASCII code for / (slash). (The parity bit, bit 8, must be 0.) Note that it is generally preferable to use only letters, numbers, underscores, and periods within file names, since the use of non-printing and other special characters can be confusing or ambiguous in certain contexts. 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. The total length of a path name Printed 4/6/89 9
INTRO(2) COMMAND REFERENCE INTRO(2) must be less than MAXPATHLEN characters. A path prefix is a path name without the final file name. If a path name begins with a slash, the path search begins at the root directory. Otherwise, the search begins from the current working directory. A slash by itself names the root directory. A null path name refers to the current directory. Directory A directory is a special type of file which contains entries which are pointers to data files or other directories. Directory entries are called links. By convention, a directory contains at least two links, . and .., referred to as dot and dot-dot respectively. Dot refers to the directory itself and dot-dot refers to its parent directory. In the root directory, .. refers to the root directory itself. 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' root directory need not be the root directory of the root file system. 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 chmod(2) call. File access is broken down according to whether a file may be read, written, or executed. Directory files use the execute permission to indicate whether the directory may be searched. 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, and 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 class of use of the caller. Read, write, and execute/search permissions on a file are granted to a process if Printed 4/6/89 10
INTRO(2) COMMAND REFERENCE INTRO(2) - the process's effective user ID is that of the superuser; - the process's effective user ID matches the user ID of the owner of the file and the ``owner'' access permissions allow the access; - 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'' access permissions allow the access; - 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 access permissions for ``other users'' allow access; - otherwise, permission is denied. Character and Block Special Files Character and block special files are used to refer to physical devices. Certain restrictions may apply to the use of character and block special files which are implementation-dependent. Sockets and Address Families A socket is an endpoint for communication between processes. Each socket has queues for sending and receiving data. 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. Each instance of the system supports some collection of socket types; consult socket(2) for more information about the types available and their properties. 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. SEE ALSO intro(3m) and perror(3c). Printed 4/6/89 11
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