1.\" $NetBSD: execve.2,v 1.17 2000/05/08 10:15:17 soda Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)execve.2 8.5 (Berkeley) 6/1/94 35.\" 36.Dd June 1, 1994 37.Dt EXECVE 2 38.Os 39.Sh NAME 40.Nm execve 41.Nd execute a file 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.Fd #include <unistd.h> 46.Ft int 47.Fn execve "const char *path" "char *const argv[]" "char *const envp[]" 48.Sh DESCRIPTION 49.Fn execve 50transforms the calling process into a new process. 51The new process is constructed from an ordinary file, 52whose name is pointed to by 53.Fa path , 54called the 55.Em new process file . 56This file is either an executable object file, 57or a file of data for an interpreter. 58An executable object file consists of an identifying header, 59followed by pages of data representing the initial program (text) 60and initialized data pages. Additional pages may be specified 61by the header to be initialized with zero data; see 62.Xr a.out 5 . 63.Pp 64An interpreter file begins with a line of the form: 65.Pp 66.Bd -filled -offset indent -compact 67.Sy \&#! 68.Em interpreter 69.Bq Em arg 70.Ed 71.Pp 72When an interpreter file is 73.\" was .Fn execve Ap d , 74\fBexecve\fP'd, 75the system 76.\" was .Fn execve Ap s 77\fBexecve\fP's 78runs the specified 79.Em interpreter . 80If the optional 81.Em arg 82is specified, it becomes the first argument to the 83.Em interpreter , 84and the name of the originally 85.\" was .Fn execve Ap d 86\fBexecve\fP'd 87file becomes the second argument; 88otherwise, the name of the originally 89.\" was .Fn execve Ap d 90\fBexecve\fP'd 91file becomes the first argument. The original arguments are shifted over to 92become the subsequent arguments. The zeroth argument, normally the name of the 93.\" was .Fn execve Ap d 94\fBexecve\fP'd 95file, is left unchanged. 96.Pp 97The argument 98.Fa argv 99is a pointer to a null-terminated array of 100character pointers to null-terminated character strings. 101These strings construct the argument list to be made available to the new 102process. At least one argument must be present in 103the array; by custom, the first element should be 104the name of the executed program (for example, the last component of 105.Fa path ) . 106.Pp 107The argument 108.Fa envp 109is also a pointer to a null-terminated array of 110character pointers to null-terminated strings. 111A pointer to this array is normally stored in the global variable 112.Va environ. 113These strings pass information to the 114new process that is not directly an argument to the command (see 115.Xr environ 7 ) . 116.Pp 117File descriptors open in the calling process image remain open in 118the new process image, except for those for which the close-on-exec 119flag is set (see 120.Xr close 2 121and 122.Xr fcntl 2 ) . 123Descriptors that remain open are unaffected by 124.Fn execve . 125.Pp 126Signals set to be ignored in the calling process are set to be ignored in 127the 128new process. Signals which are set to be caught in the calling process image 129are set to default action in the new process image. 130Blocked signals remain blocked regardless of changes to the signal action. 131The signal stack is reset to be undefined (see 132.Xr sigaction 2 133for more information). 134.Pp 135If the set-user-ID mode bit of the new process image file is set 136(see 137.Xr chmod 2 ) , 138the effective user ID of the new process image is set to the owner ID 139of the new process image file. 140If the set-group-ID mode bit of the new process image file is set, 141the effective group ID of the new process image is set to the group ID 142of the new process image file. 143(The effective group ID is the first element of the group list.) 144The real user ID, real group ID and 145other group IDs of the new process image remain the same as the calling 146process image. 147After any set-user-ID and set-group-ID processing, 148the effective user ID is recorded as the saved set-user-ID, 149and the effective group ID is recorded as the saved set-group-ID. 150These values may be used in changing the effective IDs later (see 151.Xr setuid 2 ) . 152.ne 1i 153.Pp 154The new process also inherits the following attributes from 155the calling process: 156.Pp 157.Bl -column parent_process_ID -offset indent -compact 158.It process ID Ta see Xr getpid 2 159.It parent process ID Ta see Xr getppid 2 160.It process group ID Ta see Xr getpgrp 2 161.It access groups Ta see Xr getgroups 2 162.It working directory Ta see Xr chdir 2 163.It root directory Ta see Xr chroot 2 164.It control terminal Ta see Xr termios 4 165.It resource usages Ta see Xr getrusage 2 166.It interval timers Ta see Xr getitimer 2 167.It resource limits Ta see Xr getrlimit 2 168.It file mode mask Ta see Xr umask 2 169.It signal mask Ta see Xr sigaction 2 , 170.Xr sigprocmask 2 171.El 172.Pp 173When a program is executed as a result of an 174.Fn execve 175call, it is entered as follows: 176.Bd -literal -offset indent 177main(argc, argv, envp) 178int argc; 179char **argv, **envp; 180.Ed 181.Pp 182where 183.Fa argc 184is the number of elements in 185.Fa argv 186(the ``arg count'') 187and 188.Fa argv 189points to the array of character pointers 190to the arguments themselves. 191.Sh RETURN VALUES 192As the 193.Fn execve 194function overlays the current process image 195with a new process image the successful call 196has no process to return to. 197If 198.Fn execve 199does return to the calling process an error has occurred; the 200return value will be -1 and the global variable 201.Va errno 202is set to indicate the error. 203.Sh ERRORS 204.Fn execve 205will fail and return to the calling process if: 206.Bl -tag -width Er 207.It Bq Er ENOTDIR 208A component of the path prefix is not a directory. 209.It Bq Er ENAMETOOLONG 210A component of a pathname exceeded 211.Dv {NAME_MAX} 212characters, or an entire path name exceeded 213.Dv {PATH_MAX} 214characters. 215.It Bq Er ENOENT 216The new process file does not exist. 217.It Bq Er ELOOP 218Too many symbolic links were encountered in translating the pathname. 219.It Bq Er EACCES 220Search permission is denied for a component of the path prefix. 221.It Bq Er EACCES 222The new process file is not an ordinary file. 223.It Bq Er EACCES 224The new process file mode denies execute permission. 225.It Bq Er EACCES 226The new process file is on a filesystem mounted with execution 227disabled 228.Pf ( Dv MNT_NOEXEC 229in 230.Ao Pa sys/mount.h Ac ) . 231.It Bq Er ENOEXEC 232The new process file has the appropriate access 233permission, but has an invalid magic number in its header. 234.It Bq Er ETXTBSY 235The new process file is a pure procedure (shared text) 236file that is currently open for writing or reading by some process. 237.ne 1i 238.It Bq Er ENOMEM 239The new process requires more virtual memory than 240is allowed by the imposed maximum 241.Pq Xr getrlimit 2 . 242.It Bq Er E2BIG 243The number of bytes in the new process's argument list 244is larger than the system-imposed limit. 245The limit in the system as released is 262144 bytes 246.Pf ( Dv NCARGS 247in 248.Ao Pa sys/param.h Ac ) . 249.It Bq Er EFAULT 250The new process file is not as long as indicated by 251the size values in its header. 252.It Bq Er EFAULT 253.Fa path , 254.Fa argv , 255or 256.Fa envp 257point 258to an illegal address. 259.It Bq Er EIO 260An I/O error occurred while reading from the file system. 261.El 262.Sh CAVEAT 263If a program is 264.Em setuid 265to a non-super-user, but is executed when 266the real 267.Em uid 268is ``root'', then the program has some of the powers 269of a super-user as well. 270.Sh SEE ALSO 271.Xr _exit 2 , 272.Xr fork 2 , 273.Xr execl 3 , 274.Xr environ 7 275.Sh STANDARDS 276The 277.Fn execve 278function conforms to 279.St -p1003.1-90 . 280.Sh HISTORY 281The 282.Fn execve 283function call appeared in 284.Bx 4.2 . 285