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.Fo execve 46.Fa "const char *path" 47.Fa "char *const argv[]" 48.Fa "char *const envp[]" 49.Fc 50.Sh DESCRIPTION 51.Fn execve 52transforms the calling process into a new process. 53The new process is constructed from an ordinary file, 54whose name is pointed to by 55.Fa path , 56called the 57.Em new process file . 58This file is either an executable object file, 59or a file of data for an interpreter. 60An executable object file consists of an identifying header, 61followed by pages of data representing the initial program (text) 62and initialized data pages. Additional pages may be specified 63by the header to be initialized with zero data; see 64.Xr a.out 5 . 65.Pp 66An interpreter file begins with a line of the form: 67.Pp 68.Bd -filled -offset indent -compact 69.Sy \&#! 70.Em interpreter 71.Bq Em arg ... 72.Ed 73.Pp 74When an interpreter file is 75.Fn execve Ap d , 76the system runs the specified 77.Em interpreter . 78If any optional 79.Em args 80are specified, they become the first (second, ...) argument to the 81.Em interpreter. 82The name of the originally 83.Fn execve Ap d 84file becomes the subsequent argument; 85otherwise, the name of the originally 86.Fn execve Ap d 87file is the first argument. 88The original arguments to the invocation of the interpreter 89are shifted over to become the final arguments. 90The zeroth argument, normally the name of the 91.Fn execve Ap d 92file, is left unchanged. 93.Pp 94The argument 95.Fa argv 96is a pointer to a null-terminated array of 97character pointers to null-terminated character strings. 98These strings construct the argument list to be made available to the new 99process. At least one argument must be present in 100the array; by custom, the first element should be 101the name of the executed program (for example, the last component of 102.Fa path ) . 103.Pp 104The argument 105.Fa envp 106is also a pointer to a null-terminated array of 107character pointers to null-terminated strings. 108A pointer to this array is normally stored in the global variable 109.Va environ. 110These strings pass information to the 111new process that is not directly an argument to the command (see 112.Xr environ 7 ) . 113.Pp 114File descriptors open in the calling process image remain open in 115the new process image, except for those for which the close-on-exec 116flag is set (see 117.Xr close 2 118and 119.Xr fcntl 2 ) . 120Descriptors that remain open are unaffected by 121.Fn execve . 122.Pp 123Signals set to be ignored in the calling process are set to be ignored in 124the 125new process. Signals which are set to be caught in the calling process image 126are set to default action in the new process image. 127Blocked signals remain blocked regardless of changes to the signal action. 128The signal stack is reset to be undefined (see 129.Xr sigaction 2 130for more information). 131.Pp 132If the set-user-ID mode bit of the new process image file is set 133(see 134.Xr chmod 2 ) , 135the effective user ID of the new process image is set to the owner ID 136of the new process image file. 137If the set-group-ID mode bit of the new process image file is set, 138the effective group ID of the new process image is set to the group ID 139of the new process image file. 140(The effective group ID is the first element of the group list.) 141The real user ID, real group ID and 142other group IDs of the new process image remain the same as the calling 143process image. 144After any set-user-ID and set-group-ID processing, 145the effective user ID is recorded as the saved set-user-ID, 146and the effective group ID is recorded as the saved set-group-ID. 147These values may be used in changing the effective IDs later (see 148.Xr setuid 2 ) . 149.Pp 150The new process also inherits the following attributes from 151the calling process: 152.Pp 153.Bl -column parent_process_ID -offset indent -compact 154.It process ID Ta see Xr getpid 2 155.It parent process ID Ta see Xr getppid 2 156.It process group ID Ta see Xr getpgrp 2 157.It access groups Ta see Xr getgroups 2 158.It working directory Ta see Xr chdir 2 159.It root directory Ta see Xr chroot 2 160.It control terminal Ta see Xr termios 4 161.It resource usages Ta see Xr getrusage 2 162.It interval timers Ta see Xr getitimer 2 163.It resource limits Ta see Xr getrlimit 2 164.It file mode mask Ta see Xr umask 2 165.It signal mask Ta see Xr sigaction 2 , 166.Xr sigsetmask 2 167.El 168.Pp 169When a program is executed as a result of an 170.Fn execve 171call, it is entered as follows: 172.Bd -literal -offset indent 173main(argc, argv, envp) 174int argc; 175char **argv, **envp; 176.Ed 177.Pp 178where 179.Fa argc 180is the number of elements in 181.Fa argv 182(the ``arg count'') 183and 184.Fa argv 185points to the array of character pointers 186to the arguments themselves. 187.Sh RETURN VALUES 188As the 189.Fn execve 190function overlays the current process image with a new process image, 191the successful call has no process to return to. 192If 193.Fn execve 194does return to the calling process, an error has occurred; 195the return value will be -1 and the global variable 196.Va errno 197is set to indicate the error. 198.Sh ERRORS 199.Fn execve 200will fail and return to the calling process if: 201.Bl -tag -width Er 202.\" ========== 203.It Bq Er E2BIG 204The number of bytes in the new process's argument list 205is larger than the system-imposed limit. 206This limit is specified by the 207.Xr sysctl 3 208MIB variable 209.Dv KERN_ARGMAX . 210.\" ========== 211.It Bq Er EACCES 212Search permission is denied for a component of the path prefix. 213.\" ========== 214.It Bq Er EACCES 215The new process file is not an ordinary file. 216.\" ========== 217.It Bq Er EACCES 218The new process file mode denies execute permission. 219.\" ========== 220.It Bq Er EACCES 221The new process file is on a filesystem mounted 222with execution disabled 223.Pf ( Dv MNT_NOEXEC 224in 225.Ao Pa sys/mount.h Ac ) . 226.\" ========== 227.It Bq Er EFAULT 228The new process file is not as long as indicated by 229the size values in its header. 230.\" ========== 231.It Bq Er EFAULT 232.Fa Path , 233.Fa argv , 234or 235.Fa envp 236point 237to an illegal address. 238.\" ========== 239.It Bq Er EIO 240An I/O error occurred while reading from the file system. 241.\" ========== 242.It Bq Er ELOOP 243Too many symbolic links were encountered in translating the pathname. 244This is taken to be indicative of a looping symbolic link. 245.\" ========== 246.It Bq Er ENAMETOOLONG 247A component of a pathname exceeded 248.Dv {NAME_MAX} 249characters, or an entire path name exceeded 250.Dv {PATH_MAX} 251characters. 252.\" ========== 253.It Bq Er ENOENT 254The new process file does not exist. 255.\" ========== 256.It Bq Er ENOEXEC 257The new process file has the appropriate access 258permission, but has an unrecognized format 259(e.g., an invalid magic number in its header). 260.\" ========== 261.It Bq Er ENOMEM 262The new process requires more virtual memory than 263is allowed by the imposed maximum 264.Pq Xr getrlimit 2 . 265.\" ========== 266.It Bq Er ENOTDIR 267A component of the path prefix is not a directory. 268.\" ========== 269.It Bq Er ETXTBSY 270The new process file is a pure procedure (shared text) 271file that is currently open for writing or reading by some process. 272.El 273.Sh CAVEAT 274If a program is 275.Em setuid 276to a non-super-user, but is executed when 277the real 278.Em uid 279is ``root'', then the program has some of the powers 280of a super-user as well. 281.Sh SEE ALSO 282.Xr exit 2 , 283.Xr fork 2 , 284.Xr execl 3 , 285.Xr sysctl 3 , 286.Xr environ 7 287.Sh HISTORY 288The 289.Fn execve 290function call appeared in 291.Bx 4.2 . 292