1.\" Copyright (c) 1980, 1991 Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" from: @(#)execve.2 6.9 (Berkeley) 3/10/91 33.\" $Id: execve.2,v 1.5 1993/11/29 21:25:05 jtc Exp $ 34.\" 35.Dd March 10, 1991 36.Dt EXECVE 2 37.Os BSD 4 38.Sh NAME 39.Nm execve 40.Nd execute a file 41.Sh SYNOPSIS 42.Fd #include <unistd.h> 43.Ft int 44.Fn execve "const char *path" "const * char *argv" "const * char *envp" 45.Sh DESCRIPTION 46.Fn Execve 47transforms the calling process into a new process. 48The new process is constructed from an ordinary file, 49whose name is pointed to by 50.Fa path , 51called the 52.Em new process file . 53This file is either an executable object file, 54or a file of data for an interpreter. 55An executable object file consists of an identifying header, 56followed by pages of data representing the initial program (text) 57and initialized data pages. Additional pages may be specified 58by the header to be initialized with zero data; see 59.Xr a.out 5 . 60.Pp 61An interpreter file begins with a line of the form: 62.Pp 63.Bd -filled -offset indent -compact 64.Sy \&#! 65.Em interpreter 66.Bq Em arg 67.Ed 68.Pp 69When an interpreter file is 70.Fn execve Ap d , 71the system 72.Fn execve Ap s 73the specified 74.Em interpreter . 75If the optional 76.Em arg 77is specified, it becomes the first argument to the 78.Em interpreter , 79and the name of the originally 80.Fn execve Ap d 81file becomes the second argument; 82otherwise, the name of the originally 83.Fn execve Ap d 84file becomes the first argument. The original arguments are shifted over to 85become the subsequent arguments. The zeroth argument, normally the name of the 86.Fn execve Ap d 87file, is left unchanged. 88.Pp 89The argument 90.Fa argv 91is a pointer to a null-terminated array of 92character pointers to null-terminated character strings. 93These strings construct the argument list to be made available to the new 94process. At least one argument must be present in 95the array; by custom, the first element should be 96the name of the executed program (for example, the last component of 97.Fa path ) . 98.Pp 99The argument 100.Fa envp 101is also a pointer to a null-terminated array of 102character pointers to null-terminated strings. 103A pointer to this array is normally stored in the global variable 104.Va environ. 105These strings pass information to the 106new process that is not directly an argument to the command (see 107.Xr environ 7 ) . 108.Pp 109File descriptors open in the calling process image remain open in 110the new process image, except for those for which the close-on-exec 111flag is set (see 112.Xr close 2 113and 114.Xr fcntl 2 ) . 115Descriptors that remain open are unaffected by 116.Fn execve . 117.Pp 118Signals set to be ignored in the calling process are set to be ignored in 119the 120new process. Signals which are set to be caught in the calling process image 121are set to default action in the new process image. 122Blocked signals remain blocked regardless of changes to the signal action. 123The signal stack is reset to be undefined (see 124.Xr sigaction 2 125for more information). 126.Pp 127If the set-user-ID mode bit of the new process image file is set 128(see 129.Xr chmod 2 ) , 130the effective user ID of the new process image is set to the owner ID 131of the new process image file. 132If the set-group-ID mode bit of the new process image file is set, 133the effective group ID of the new process image is set to the group ID 134of the new process image file. 135The real user ID, real group ID and 136supplementary group IDs of the new process image remain the same as the calling 137process image. 138.Pp 139The new process also inherits the following attributes from 140the calling process: 141.Pp 142.Bl -column parent_process_ID -offset indent -compact 143.It process ID Ta see Xr getpid 2 144.It parent process ID Ta see Xr getppid 2 145.It process group ID Ta see Xr getpgrp 2 146.It access groups Ta see Xr getgroups 2 147.It working directory Ta see Xr chdir 2 148.It root directory Ta see Xr chroot 2 149.It control terminal Ta see Xr termios 4 150.It resource usages Ta see Xr getrusage 2 151.It interval timers Ta see Xr getitimer 2 152.It resource limits Ta see Xr getrlimit 2 153.It file mode mask Ta see Xr umask 2 154.It signal mask Ta see Xr sigvec 2 , 155.Xr sigsetmask 2 156.El 157.Pp 158When a program is executed as a result of an 159.Fn execve 160call, it is entered as follows: 161.Bd -literal -offset indent 162main(argc, argv, envp) 163int argc; 164char **argv, **envp; 165.Ed 166.Pp 167where 168.Fa argc 169is the number of elements in 170.Fa argv 171(the ``arg count'') 172and 173.Fa argv 174points to the array of character pointers 175to the arguments themselves. 176.Sh RETURN VALUES 177As the 178.Fn execve 179function overlays the current process image 180with a new process image the successful call 181has no process to return to. 182If 183.Fn execve 184does return to the calling process an error has occurred; the 185return value will be -1 and the global variable 186.Va errno 187is set to indicate the error. 188.Sh ERRORS 189.Fn Execve 190will fail and return to the calling process if: 191.Bl -tag -width Er 192.It Bq Er ENOTDIR 193A component of the path prefix is not a directory. 194.It Bq Er EINVAL 195The pathname contains a character with the high-order bit set. 196.It Bq Er ENAMETOOLONG 197A component of a pathname exceeded 255 characters, 198or an entire path name exceeded 1023 characters. 199.It Bq Er ENOENT 200The new process file does not exist. 201.It Bq Er ELOOP 202Too many symbolic links were encountered in translating the pathname. 203.It Bq Er EACCES 204Search permission is denied for a component of the path prefix. 205.It Bq Er EACCES 206The new process file is not an ordinary file. 207.It Bq Er EACCES 208The new process file mode denies execute permission. 209.It Bq Er EACCES 210The new process file is on a filesystem mounted with execution 211disabled 212.Pf ( Dv MNT_NOEXEC 213in 214.Ao Pa sys/mount.h Ac ) . 215.It Bq Er ENOEXEC 216The new process file has the appropriate access 217permission, but has an invalid magic number in its header. 218.It Bq Er ETXTBSY 219The new process file is a pure procedure (shared text) 220file that is currently open for writing or reading by some process. 221.It Bq Er ENOMEM 222The new process requires more virtual memory than 223is allowed by the imposed maximum 224.Pq Xr getrlimit 2 . 225.It Bq Er E2BIG 226The number of bytes in the new process's argument list 227is larger than the system-imposed limit. 228The limit in the system as released is 20480 bytes 229.Pf ( Dv NCARGS 230in 231.Ao Pa sys/param.h Ac ) . 232.It Bq Er EFAULT 233The new process file is not as long as indicated by 234the size values in its header. 235.It Bq Er EFAULT 236.Fa Path , 237.Fa argv , 238or 239.Fa envp 240point 241to an illegal address. 242.It Bq Er EIO 243An I/O error occurred while reading from the file system. 244.El 245.Sh CAVEAT 246If a program is 247.Em setuid 248to a non-super-user, but is executed when 249the real 250.Em uid 251is ``root'', then the program has some of the powers 252of a super-user as well. 253.Sh SEE ALSO 254.Xr exit 2 , 255.Xr fork 2 , 256.Xr execl 3 , 257.Xr environ 7 258.Sh HISTORY 259The 260.Fn execve 261function call appeared in 262.Bx 4.2 . 263