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System calls and libraries

System call error handling

System calls that fail to complete successfully almost always return a value of -1 to your program. (If you look through the system calls in Section 2, you will see that there are a few calls for which no return value is defined, but they are the exceptions.) In addition to the -1 returned to the program, the unsuccessful system call places an integer in an externally declared variable, errno. In a C program, you can determine the value in errno if your program contains the following statement:

#include <errno.h>

The C language function perror(3C) can be used to print an error message (on stderr) based on the value of errno. The value in errno is not cleared on successful calls, so your program should check it only if the system call returned a -1 indicating an error. The following list identifies the error numbers and symbolic names defined in the <errno.h> header file, and described in intro(2).


1 EPERM
Not privileged. Typically this error indicates an attempt to modify a file in some way forbidden except to its owner or a process with the appropriate privilege. It is also returned for attempts by ordinary users to do things allowed only to the super-user.

2 ENOENT
No such file or directory. A file name is specified and the file should exist but fails to, or one of the directories in a path name fails to exist.

3 ESRCH
No such process. No process can be found corresponding to the that specified by PID in thekill orptrace routine.

4 EINTR
Interrupted system call. An asynchronous signal (such as interrupt or quit), which the user has elected to catch, occurred during a system service routine. If execution is resumed after processing the signal, it will appear as if the interrupted routine call returned this error condition.

5 EIO
I/O error. Some physical I/O error has occurred. This error may in some cases occur on a call following the one to which it actually applies.

6 ENXIO
No such device or address. I/O on a special file refers to a subdevice which does not exist, or exists beyond the limit of the device. It may also occur when, for example, a tape drive is not on-line or no disk pack is loaded on a drive.

7 E2BIG
Arg list too long. An argument list longer than ARG_MAX bytes is presented to a member of the exec family of routines. The argument list limit is sum of the size of the argument list plus the size of the environment's exported shell variables.

8 ENOEXEC
Exec format error. A request is made to execute a file which, although it has the appropriate permissions, does not start with a valid format (see a.out(4)).

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 that is open only for writing (respectively, reading).

10 ECHILD
No child processes. A wait routine was executed by a process that had no existing or unwaited-for child processes.

11 EAGAIN
Resource is temporarily unavailable. For example, the fork routine failed because the system's process table is full or the user is not allowed to create any more processes. Or a system call failed because of insufficient memory or swap space.

12 ENOMEM
Not enough space. During execution of an exec, brk, or sbrk routine, a program asks for more space than the system is able to supply. This is not a temporary condition; the maximum size is a system parameter. The error may also occur if the arrangement of text, data, and stack segments requires too many segmentation registers, or if there is not enough swap space during thefork routine.

13 EACCES
Permission denied. An attempt was made to access a file in a way forbidden by the protection system.

14 EFAULT
Bad address. The system encountered a hardware fault in attempting to use an argument of a routine. For example,errno potentially may be set toEFAULT any time a routine that takes a pointer argument is passed an invalid address, if the system can detect the condition. Because systems will differ in their ability to reliably detect a bad address, on some implementations passing a bad address to a routine will result in undefined behavior.

15 ENOTBLK
Block device required. A non-block file was mentioned where a block device was required (for example, in a call to the mount routine).

16 EBUSY
Device busy. An attempt was made to mount a device that was already mounted or an attempt was made to dismount a device on which there is an active file (open file, current directory, mounted-on file, active text segment). It will also occur if an attempt is made to enable accounting when it is already enabled. The device or resource is currently unavailable.

17 EEXIST
File exists. An existing file was mentioned in an inappropriate context (for example, call to the link routine).

18 EXDEV
Cross-device link. A link to a file on another device was attempted.

19 ENODEV
No such device. An attempt was made to apply an inappropriate operation to a device (for example, 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 prefix or as an argument to the chdir routine).

21 EISDIR
Is a directory. An attempt was made to write on a directory.

22 EINVAL
Invalid argument. An invalid argument was specified (for example, unmounting a non-mounted device, mentioning an undefined signal in a call to the signal or kill routine. Also set by the functions described in the math package (3M).

23 ENFILE
File table overflow. The system file table is full (that is, SYS_OPEN files are open, and temporarily no more files can be opened).

24 EMFILE
Too many open files. No process may have more than OPEN_MAX file descriptors open at a time.

25 ENOTTY
Not a typewriter. A call was made to theioctl routine specifying a file that is not a special character device.

26 ETXTBSY
Text file busy. An attempt was made to execute a pure-procedure program that is currently open for writing. Also an attempt to open for writing or to remove a pure-procedure program that is being executed.

27 EFBIG
File too large. The size of a file exceeded the maximum file size, FCHR_MAX (see getrlimit(2)).

28 ENOSPC
No space left on device. While writing an ordinary file or creating a directory entry, there is no free space left on the device. In thefcntl routine, the setting or removing of record locks on a file cannot be accomplished because there are no more record entries left on the system.

29 ESPIPE
Illegal seek. A call to the lseek routine was issued to a pipe.

30 EROFS
Read-only file system. An attempt to modify a file or directory was made on a device mounted read-only.

31 EMLINK
Too many links. An attempt to make more than the maximum number of links, LINK_MAX, to a file.

32 EPIPE
Broken pipe. A write on a pipe 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 domain of func. The argument of a function in the math package (3M) is out of the domain of the function.

34 ERANGE
Math result not representable. The value of a function in the math package (3M) is not representable within machine precision.

35 ENOMSG
No message of desired type. An attempt was made to receive a message of a type not existing on the specified message queue (see msgop(2)).

36 EIDRM
Identifier removed. This error is returned to processes that resume execution due to the removal of an identifier from the file system's name space (see msgctl(2), semctl(2), and shmctl(2)).

37 ECHRNG
Channel number out of range.

38 EL2NSYNC
Level 2 not synchronized.

39 EL3HLT
Level 3 halted.

40 EL3RST
Level 3 reset.

41 ELNRNG
Link number out of range.

42 EUNATCH
Protocol driver not attached.

43 ENOCSI
No CSI structure available.

44 EL2HLT
Level 2 halted.

45 EDEADLK
Deadlock condition. A deadlock situation was detected and avoided. This error pertains to file and record locking.

46 ENOLCK
No record locks available. There are no more locks available. The system lock table is full (see fcntl(2)).

60 ENOSTR
Device not a stream. A putmsg orgetmsg system call was attempted on a file descriptor that is not aSTREAMS device.

61 ENODATA
No data available.

62 ETIME
Timer expired. The timer set for aSTREAMSioctl call has expired. The cause of this error is device specific and could indicate either a hardware or software failure, or perhaps a timeout value that is too short for the specific operation. The status of theioctl operation is indeterminate.

63 ENOSR
Out of stream resources. During a STREAMSopen, either no STREAMS queues or no STREAMS head data structures were available. This is a temporary condition; one may recover from it if other processes release resources.

65 ENOPKG
Package not installed. This error occurs when users attempt to use a system call from a package which has not been installed.

71 EPROTO
Protocol error. Some protocol error occurred. This error is device specific, but is generally not related to a hardware failure.

77 EBADMSG
Not a data message. During aread,getmsg, orioctlI_RECVFD system call to aSTREAMS device, something has come to the head of the queue that cannot be processed. That something depends on the system call: read: control information or a passed file descriptor. getmsg: passed file descriptor. ioctl: control or data information.

78 ENAMETOOLONG
File name too long. The length of the path argument exceedsPATH_MAX, or the length of a path component exceedsNAME_MAX while _POSIX_NO_TRUNC is in effect; (see limits(4)).

79 EOVERFLOW
Value too large to be stored in data type.

80 ENOTUNIQ
Name not unique on network. Given log name not unique.

81 EBADFD
File descriptor in bad state. Either a file descriptor refers to no open file or a read request was made to a file that is open only for writing.

82 EREMCHG
Remote address changed.

83 ELIBACC
Cannot access a needed shared library. Trying toexec ana.out that requires a shared library and the shared library doesn't exist or the user doesn't have permission to use it.

84 ELIBBAD
Accessing a corrupted shared library. Trying toexec ana.out that requires a shared library (to be linked in) andexec could not load the shared library. The shared library is probably corrupted.

85 ELIBSCN
.lib section ina.out corrupted Trying toexec ana.out that requires a shared library (to be linked in) and there was erroneous data in the.lib section of thea.out. The.lib section tellsexec what shared libraries are needed. Thea.out is probably corrupted.

86 ELIBMAX
Attempting to link in more shared libraries than system limit. Trying toexec ana.out that requires more static shared libraries than is allowed on the current configuration of the system. See ``Managing system performance''.

87 ELIBEXEC
Cannotexec a shared library directly. Attempting toexec a shared library directly.

88 EILSEQ
Illegal byte sequence. Handle multiple characters as a single character.

89 ENOSYS
Operation not applicable.

90 ELOOP
Number of symbolic links encountered during path name traversal exceedsMAXSYMLINKS

91 ERESTART
Interrupted system call should be restarted.

92 ESTRPIPE
Streams pipe error (not externally visible).

93 ENOTEMPTY
Directory not empty.

94 EUSERS
Too many users. Too many users.

95 ENOTSOCK
Socket operation on non-socket. Self-explanatory.

96 EDESTADDRREQ
Destination address required. A required address was omitted from an operation on a transport endpoint. Destination address required.

97 EMSGSIZE
Message too long. A message sent on a transport provider was larger than the internal message buffer or some other network limit.

98 EPROTOTYPE
Protocol wrong type for socket. A protocol was specified that does not support the semantics of the socket type requested.

99 ENOPROTOOPT
Protocol not available. A bad option or level was specified when getting or setting options for a protocol.

120 EPROTONOSUPPORT
Protocol not supported. The protocol has not been configured into the system or no implementation for it exists.

121 ESOCKTNOSUPPORT
Socket type not supported. The support for the socket type has not been configured into the system or no implementation for it exists.

122 EOPNOTSUPP
Operation not supported on transport endpoint. For example, trying to accept a connection on a datagram transport endpoint.

123 EPFNOSUPPORT
Protocol family not supported. The protocol family has not been configured into the system or no implementation for it exists. Used for the Internet protocols.

124 EAFNOSUPPORT
Address family not supported by protocol family. An address incompatible with the requested protocol was used.

125 EADDRINUSE
Address already in use. User attempted to use an address already in use, and the protocol does not allow this.

126 EADDRNOTAVAIL
Cannot assign requested address. Results from an attempt to create a transport endpoint with an address not on the current machine.

127 ENETDOWN
Network is down. Operation encountered a dead network.

128 ENETUNREACH
Network is unreachable. Operation was attempted to an unreachable network.

129 ENETRESET
Network dropped connection because of reset. The host you were connected to crashed and rebooted.

130 ECONNABORTED
Software caused connection abort. A connection abort was caused internal to your host machine.

131 ECONNRESET
Connection reset by peer. A connection was forcibly closed by a peer. This normally results from a loss of the connection on the remote host due to a timeout or a reboot.

132 ENOBUFS
No buffer space available. An operation on a transport endpoint or pipe was not performed because the system lacked sufficient buffer space or because a queue was full.

133 EISCONN
Transport endpoint is already connected. A connect request was made on an already connected transport endpoint; or, asendto orsendmsg request on a connected transport endpoint specified a destination when already connected.

134 ENOTCONN
Transport endpoint is not connected. A request to send or receive data was disallowed because the transport endpoint is not connected and (when sending a datagram) no address was supplied.

143 ESHUTDOWN
Cannot send after transport endpoint shutdown. A request to send data was disallowed because the transport endpoint had already been shut down.

144 ETOOMANYREFS
Too many references: cannot splice.

145 ETIMEDOUT
Connection timed out. A connect or send request failed because the connected party did not properly respond after a period of time. (The timeout period is dependent on the communication protocol.)

146 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 that is inactive on the remote host.

147 EHOSTDOWN
Host is down. A transport provider operation failed because the destination host was down.

148 EHOSTUNREACH
No route to host. A transport provider operation was attempted to an unreachable host.

149 EALREADY
Operation already in progress. An operation was attempted on a non-blocking object that already had an operation in progress.

150 EINPROGRESS
Operation now in progress. An operation that takes a long time to complete (such as aconnect) was attempted on a non-blocking object.

151 ESTALE
Stale NFS file handle.

152 ENOLOAD
Cannot load required module. An attempt made to load a module failed.

153 ERELOC
Relocation error in loading module. Symbolic referencing error.

154 ENOMATCH
No symbol is found matching the given spec.

156 EBADVER
Version number mis-matched. The version number associated with a module is not supported by the kernel.

157 ECONFIG
Configured kernel resource exhausted.

158 ECANCELLED
Asynchronous I/O cancelled.

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