1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. 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.\" @(#)execve.2 8.5 (Berkeley) 6/1/94 33.\" $FreeBSD$ 34.\" 35.Dd June 1, 1994 36.Dt EXECVE 2 37.Os 38.Sh NAME 39.Nm execve 40.Nd execute a file 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In unistd.h 45.Ft int 46.Fn execve "const char *path" "char *const argv[]" "char *const envp[]" 47.Sh DESCRIPTION 48The 49.Fn execve 50function 51transforms the calling process into a new process. 52The new process is constructed from an ordinary file, 53whose name is pointed to by 54.Fa path , 55called the 56.Em new process file . 57This file is either an executable object file, 58or a file of data for an interpreter. 59An executable object file consists of an identifying header, 60followed by pages of data representing the initial program (text) 61and initialized data pages. Additional pages may be specified 62by the header to be initialized with zero data; see 63.Xr elf 5 64and 65.Xr a.out 5 . 66.Pp 67An interpreter file begins with a line of the form: 68.Pp 69.Bd -ragged -offset indent -compact 70.Sy \&#! 71.Em interpreter 72.Bq Em arg 73.Ed 74.Pp 75When an interpreter file is 76.Sy execve Ap d , 77the system actually 78.Sy execve Ap s 79the specified 80.Em interpreter . 81If the optional 82.Em arg 83is specified, it becomes the first argument to the 84.Em interpreter , 85and the name of the originally 86.Sy execve Ap d 87file becomes the second argument; 88otherwise, the name of the originally 89.Sy execve Ap d 90file becomes the first argument. The original arguments are shifted over to 91become the subsequent arguments. 92The zeroth argument is set to the specified 93.Em interpreter . 94.Pp 95The argument 96.Fa argv 97is a pointer to a null-terminated array of 98character pointers to null-terminated character strings. 99These strings construct the argument list to be made available to the new 100process. At least one argument must be present in 101the array; by custom, the first element should be 102the name of the executed program (for example, the last component of 103.Fa path ) . 104.Pp 105The argument 106.Fa envp 107is also a pointer to a null-terminated array of 108character pointers to null-terminated strings. 109A pointer to this array is normally stored in the global variable 110.Va environ . 111These strings pass information to the 112new process that is not directly an argument to the command (see 113.Xr environ 7 ) . 114.Pp 115File descriptors open in the calling process image remain open in 116the new process image, except for those for which the close-on-exec 117flag is set (see 118.Xr close 2 119and 120.Xr fcntl 2 ) . 121Descriptors that remain open are unaffected by 122.Fn execve . 123.Pp 124Signals set to be ignored in the calling process are set to be ignored in 125the 126new process. 127Signals which are set to be caught in the calling process image 128are set to default action in the new process image. 129Blocked signals remain blocked regardless of changes to the signal action. 130The signal stack is reset to be undefined (see 131.Xr sigaction 2 132for more information). 133.Pp 134If the set-user-ID mode bit of the new process image file is set 135(see 136.Xr chmod 2 ) , 137the effective user ID of the new process image is set to the owner ID 138of the new process image file. 139If the set-group-ID mode bit of the new process image file is set, 140the effective group ID of the new process image is set to the group ID 141of the new process image file. 142(The effective group ID is the first element of the group list.) 143The real user ID, real group ID and 144other group IDs of the new process image remain the same as the calling 145process image. 146After any set-user-ID and set-group-ID processing, 147the effective user ID is recorded as the saved set-user-ID, 148and the effective group ID is recorded as the saved set-group-ID. 149These values may be used in changing the effective IDs later (see 150.Xr setuid 2 ) . 151.Pp 152The set-ID bits are not honored if the respective file system has the 153.Ar nosuid 154option enabled or if the new process file is an interpreter file. Syscall 155tracing is disabled if effective IDs are changed. 156.Pp 157The new process also inherits the following attributes from 158the calling process: 159.Pp 160.Bl -column parent_process_ID -offset indent -compact 161.It process ID Ta see Xr getpid 2 162.It parent process ID Ta see Xr getppid 2 163.It process group ID Ta see Xr getpgrp 2 164.It access groups Ta see Xr getgroups 2 165.It working directory Ta see Xr chdir 2 166.It root directory Ta see Xr chroot 2 167.It control terminal Ta see Xr termios 4 168.It resource usages Ta see Xr getrusage 2 169.It interval timers Ta see Xr getitimer 2 170.It resource limits Ta see Xr getrlimit 2 171.It file mode mask Ta see Xr umask 2 172.It signal mask Ta see Xr sigvec 2 , 173.Xr sigsetmask 2 174.El 175.Pp 176When a program is executed as a result of an 177.Fn execve 178call, it is entered as follows: 179.Bd -literal -offset indent 180main(argc, argv, envp) 181int argc; 182char **argv, **envp; 183.Ed 184.Pp 185where 186.Fa argc 187is the number of elements in 188.Fa argv 189(the ``arg count'') 190and 191.Fa argv 192points to the array of character pointers 193to the arguments themselves. 194.Sh RETURN VALUES 195As the 196.Fn execve 197function overlays the current process image 198with a new process image the successful call 199has no process to return to. 200If 201.Fn execve 202does return to the calling process an error has occurred; the 203return value will be -1 and the global variable 204.Va errno 205is set to indicate the error. 206.Sh ERRORS 207The 208.Fn execve 209function 210will fail and return to the calling process if: 211.Bl -tag -width Er 212.It Bq Er ENOTDIR 213A component of the path prefix is not a directory. 214.It Bq Er ENAMETOOLONG 215A component of a pathname exceeded 255 characters, 216or an entire path name exceeded 1023 characters. 217.It Bq Er ENAMETOOLONG 218When invoking an interpreted script, the interpreter name 219exceeds 220.Dv MAXSHELLCMDLEN 221characters. 222.It Bq Er ENOENT 223The new process file does not exist. 224.It Bq Er ELOOP 225Too many symbolic links were encountered in translating the pathname. 226.It Bq Er EACCES 227Search permission is denied for a component of the path prefix. 228.It Bq Er EACCES 229The new process file is not an ordinary file. 230.It Bq Er EACCES 231The new process file mode denies execute permission. 232.It Bq Er ENOEXEC 233The new process file has the appropriate access 234permission, but has an invalid magic number in its header. 235.It Bq Er ETXTBSY 236The new process file is a pure procedure (shared text) 237file that is currently open for writing or reading by some process. 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' argument list 244is larger than the system-imposed limit. 245This limit is specified by the 246.Xr sysctl 3 247MIB variable 248.Dv KERN_ARGMAX . 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 ktrace 1 , 272.Xr fork 2 , 273.Xr _exit 2 , 274.Xr execl 3 , 275.Xr exit 3 , 276.Xr sysctl 3 , 277.Xr a.out 5 , 278.Xr elf 5 , 279.Xr environ 7 , 280.Xr mount 8 281.Sh HISTORY 282The 283.Fn execve 284function call appeared in 285.Bx 4.2 . 286