1.\" $NetBSD: execve.2,v 1.9 1995/02/27 12:32:25 cgd 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 8.3 (Berkeley) 1/24/94 35.\" 36.Dd January 24, 1994 37.Dt EXECVE 2 38.Os BSD 4 39.Sh NAME 40.Nm execve 41.Nd execute a file 42.Sh SYNOPSIS 43.Fd #include <unistd.h> 44.Ft int 45.Fn execve "const char *path" "char *const argv[]" "char *const envp[]" 46.Sh DESCRIPTION 47.Fn Execve 48transforms the calling process into a new process. 49The new process is constructed from an ordinary file, 50whose name is pointed to by 51.Fa path , 52called the 53.Em new process file . 54This file is either an executable object file, 55or a file of data for an interpreter. 56An executable object file consists of an identifying header, 57followed by pages of data representing the initial program (text) 58and initialized data pages. Additional pages may be specified 59by the header to be initialized with zero data; see 60.Xr a.out 5 . 61.Pp 62An interpreter file begins with a line of the form: 63.Pp 64.Bd -filled -offset indent -compact 65.Sy \&#! 66.Em interpreter 67.Bq Em arg 68.Ed 69.Pp 70When an interpreter file is 71.Fn execve Ap d , 72the system 73.Fn execve Ap s 74runs the specified 75.Em interpreter . 76If the optional 77.Em arg 78is specified, it becomes the first argument to the 79.Em interpreter , 80and the name of the originally 81.Fn execve Ap d 82file becomes the second argument; 83otherwise, the name of the originally 84.Fn execve Ap d 85file becomes the first argument. The original arguments are shifted over to 86become the subsequent arguments. The zeroth argument, normally the name of the 87.Fn execve Ap d 88file, is left unchanged. 89.Pp 90The argument 91.Fa argv 92is a pointer to a null-terminated array of 93character pointers to null-terminated character strings. 94These strings construct the argument list to be made available to the new 95process. At least one argument must be present in 96the array; by custom, the first element should be 97the name of the executed program (for example, the last component of 98.Fa path ) . 99.Pp 100The argument 101.Fa envp 102is also a pointer to a null-terminated array of 103character pointers to null-terminated strings. 104A pointer to this array is normally stored in the global variable 105.Va environ. 106These strings pass information to the 107new process that is not directly an argument to the command (see 108.Xr environ 7 ) . 109.Pp 110File descriptors open in the calling process image remain open in 111the new process image, except for those for which the close-on-exec 112flag is set (see 113.Xr close 2 114and 115.Xr fcntl 2 ) . 116Descriptors that remain open are unaffected by 117.Fn execve . 118.Pp 119Signals set to be ignored in the calling process are set to be ignored in 120the 121new process. Signals which are set to be caught in the calling process image 122are set to default action in the new process image. 123Blocked signals remain blocked regardless of changes to the signal action. 124The signal stack is reset to be undefined (see 125.Xr sigaction 2 126for more information). 127.Pp 128If the set-user-ID mode bit of the new process image file is set 129(see 130.Xr chmod 2 ) , 131the effective user ID of the new process image is set to the owner ID 132of the new process image file. 133If the set-group-ID mode bit of the new process image file is set, 134the effective group ID of the new process image is set to the group ID 135of the new process image file. 136(The effective group ID is the first element of the group list.) 137The real user ID, real group ID and 138other group IDs of the new process image remain the same as the calling 139process image. 140After any set-user-ID and set-group-ID processing, 141the effective user ID is recorded as the saved set-user-ID, 142and the effective group ID is recorded as the saved set-group-ID. 143These values may be used in changing the effective IDs later (see 144.Xr setuid 2 ) . 145.Pp 146The new process also inherits the following attributes from 147the calling process: 148.Pp 149.Bl -column parent_process_ID -offset indent -compact 150.It process ID Ta see Xr getpid 2 151.It parent process ID Ta see Xr getppid 2 152.It process group ID Ta see Xr getpgrp 2 153.It access groups Ta see Xr getgroups 2 154.It working directory Ta see Xr chdir 2 155.It root directory Ta see Xr chroot 2 156.It control terminal Ta see Xr termios 4 157.It resource usages Ta see Xr getrusage 2 158.It interval timers Ta see Xr getitimer 2 159.It resource limits Ta see Xr getrlimit 2 160.It file mode mask Ta see Xr umask 2 161.It signal mask Ta see Xr sigaction 2 , 162.Xr sigsetmask 2 163.El 164.Pp 165When a program is executed as a result of an 166.Fn execve 167call, it is entered as follows: 168.Bd -literal -offset indent 169main(argc, argv, envp) 170int argc; 171char **argv, **envp; 172.Ed 173.Pp 174where 175.Fa argc 176is the number of elements in 177.Fa argv 178(the ``arg count'') 179and 180.Fa argv 181points to the array of character pointers 182to the arguments themselves. 183.Sh RETURN VALUES 184As the 185.Fn execve 186function overlays the current process image 187with a new process image the successful call 188has no process to return to. 189If 190.Fn execve 191does return to the calling process an error has occurred; the 192return value will be -1 and the global variable 193.Va errno 194is set to indicate the error. 195.Sh ERRORS 196.Fn Execve 197will fail and return to the calling process if: 198.Bl -tag -width Er 199.It Bq Er ENOTDIR 200A component of the path prefix is not a directory. 201.It Bq Er ENAMETOOLONG 202A component of a pathname exceeded 203.Dv {NAME_MAX} 204characters, or an entire path name exceeded 205.Dv {PATH_MAX} 206characters. 207.It Bq Er ENOENT 208The new process file does not exist. 209.It Bq Er ELOOP 210Too many symbolic links were encountered in translating the pathname. 211.It Bq Er EACCES 212Search permission is denied for a component of the path prefix. 213.It Bq Er EACCES 214The new process file is not an ordinary file. 215.It Bq Er EACCES 216The new process file mode denies execute permission. 217.It Bq Er EACCES 218The new process file is on a filesystem mounted with execution 219disabled 220.Pf ( Dv MNT_NOEXEC 221in 222.Ao Pa sys/mount.h Ac ) . 223.It Bq Er ENOEXEC 224The new process file has the appropriate access 225permission, but has an invalid magic number in its header. 226.It Bq Er ETXTBSY 227The new process file is a pure procedure (shared text) 228file that is currently open for writing or reading by some process. 229.It Bq Er ENOMEM 230The new process requires more virtual memory than 231is allowed by the imposed maximum 232.Pq Xr getrlimit 2 . 233.It Bq Er E2BIG 234The number of bytes in the new process's argument list 235is larger than the system-imposed limit. 236The limit in the system as released is 20480 bytes 237.Pf ( Dv NCARGS 238in 239.Ao Pa sys/param.h Ac ) . 240.It Bq Er EFAULT 241The new process file is not as long as indicated by 242the size values in its header. 243.It Bq Er EFAULT 244.Fa Path , 245.Fa argv , 246or 247.Fa envp 248point 249to an illegal address. 250.It Bq Er EIO 251An I/O error occurred while reading from the file system. 252.El 253.Sh CAVEAT 254If a program is 255.Em setuid 256to a non-super-user, but is executed when 257the real 258.Em uid 259is ``root'', then the program has some of the powers 260of a super-user as well. 261.Sh SEE ALSO 262.Xr exit 2 , 263.Xr fork 2 , 264.Xr execl 3 , 265.Xr environ 7 266.Sh HISTORY 267The 268.Fn execve 269function call appeared in 270.Bx 4.2 . 271