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 BSD 4 38.Sh NAME 39.Nm execve 40.Nd execute a file 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.Fd #include <unistd.h> 45.Ft int 46.Fn execve "const char *path" "char *const argv[]" "char *const envp[]" 47.Sh DESCRIPTION 48.Fn Execve 49transforms the calling process into a new process. 50The new process is constructed from an ordinary file, 51whose name is pointed to by 52.Fa path , 53called the 54.Em new process file . 55This file is either an executable object file, 56or a file of data for an interpreter. 57An executable object file consists of an identifying header, 58followed by pages of data representing the initial program (text) 59and initialized data pages. Additional pages may be specified 60by the header to be initialized with zero data; see 61.Xr elf 5 62and 63.Xr a.out 5 . 64.Pp 65An interpreter file begins with a line of the form: 66.Pp 67.Bd -filled -offset indent -compact 68.Sy \&#! 69.Em interpreter 70.Bq Em arg 71.Ed 72.Pp 73When an interpreter file is 74.Sy execve Ap d , 75the system actually 76.Sy execve Ap s 77the specified 78.Em interpreter . 79If the optional 80.Em arg 81is specified, it becomes the first argument to the 82.Em interpreter , 83and the name of the originally 84.Sy execve Ap d 85file becomes the second argument; 86otherwise, the name of the originally 87.Sy execve Ap d 88file becomes the first argument. The original arguments are shifted over to 89become the subsequent arguments. 90The zeroth argument is set to the specified 91.Em interpreter . 92.Pp 93The argument 94.Fa argv 95is a pointer to a null-terminated array of 96character pointers to null-terminated character strings. 97These strings construct the argument list to be made available to the new 98process. At least one argument must be present in 99the array; by custom, the first element should be 100the name of the executed program (for example, the last component of 101.Fa path ) . 102.Pp 103The argument 104.Fa envp 105is also a pointer to a null-terminated array of 106character pointers to null-terminated strings. 107A pointer to this array is normally stored in the global variable 108.Va environ. 109These strings pass information to the 110new process that is not directly an argument to the command (see 111.Xr environ 7 ) . 112.Pp 113File descriptors open in the calling process image remain open in 114the new process image, except for those for which the close-on-exec 115flag is set (see 116.Xr close 2 117and 118.Xr fcntl 2 ) . 119Descriptors that remain open are unaffected by 120.Fn execve . 121.Pp 122Signals set to be ignored in the calling process are set to be ignored in 123the 124new process. 125Signals 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 set-ID bits are not honored if the respective file system has the 151.Ar nosuid 152option enabled or if the new process file is an interpreter file. Syscall 153tracing is disabled if effective IDs are changed. 154.Pp 155The new process also inherits the following attributes from 156the calling process: 157.Pp 158.Bl -column parent_process_ID -offset indent -compact 159.It process ID Ta see Xr getpid 2 160.It parent process ID Ta see Xr getppid 2 161.It process group ID Ta see Xr getpgrp 2 162.It access groups Ta see Xr getgroups 2 163.It working directory Ta see Xr chdir 2 164.It root directory Ta see Xr chroot 2 165.It control terminal Ta see Xr termios 4 166.It resource usages Ta see Xr getrusage 2 167.It interval timers Ta see Xr getitimer 2 168.It resource limits Ta see Xr getrlimit 2 169.It file mode mask Ta see Xr umask 2 170.It signal mask Ta see Xr sigvec 2 , 171.Xr sigsetmask 2 172.El 173.Pp 174When a program is executed as a result of an 175.Fn execve 176call, it is entered as follows: 177.Bd -literal -offset indent 178main(argc, argv, envp) 179int argc; 180char **argv, **envp; 181.Ed 182.Pp 183where 184.Fa argc 185is the number of elements in 186.Fa argv 187(the ``arg count'') 188and 189.Fa argv 190points to the array of character pointers 191to the arguments themselves. 192.Sh IMPLEMENTATION NOTES 193.Pp 194In the non-threaded library 195.Fn execve 196is implemented as the 197.Va execve 198syscall. 199.Pp 200In the threaded library, the 201.Va execve 202syscall is assembled to 203.Fn _thread_sys_execve 204and 205.Fn execve 206is implemented as a function which performs user-thread 207library re-initialization and then calls 208.Fn _thread_sys_execve . 209.Sh RETURN VALUES 210As the 211.Fn execve 212function overlays the current process image 213with a new process image the successful call 214has no process to return to. 215If 216.Fn execve 217does return to the calling process an error has occurred; the 218return value will be -1 and the global variable 219.Va errno 220is set to indicate the error. 221.Sh ERRORS 222.Fn Execve 223will fail and return to the calling process if: 224.Bl -tag -width Er 225.It Bq Er ENOTDIR 226A component of the path prefix is not a directory. 227.It Bq Er ENAMETOOLONG 228A component of a pathname exceeded 255 characters, 229or an entire path name exceeded 1023 characters. 230.It Bq Er ENOENT 231The new process file does not exist. 232.It Bq Er ELOOP 233Too many symbolic links were encountered in translating the pathname. 234.It Bq Er EACCES 235Search permission is denied for a component of the path prefix. 236.It Bq Er EACCES 237The new process file is not an ordinary file. 238.It Bq Er EACCES 239The new process file mode denies execute permission. 240.It Bq Er ENOEXEC 241The new process file has the appropriate access 242permission, but has an invalid magic number in its header. 243.It Bq Er ETXTBSY 244The new process file is a pure procedure (shared text) 245file that is currently open for writing or reading by some process. 246.It Bq Er ENOMEM 247The new process requires more virtual memory than 248is allowed by the imposed maximum 249.Pq Xr getrlimit 2 . 250.It Bq Er E2BIG 251The number of bytes in the new process' argument list 252is larger than the system-imposed limit. 253This limit is specified by the 254.Xr sysctl 3 255MIB variable 256.Dv KERN_ARGMAX . 257.It Bq Er EFAULT 258The new process file is not as long as indicated by 259the size values in its header. 260.It Bq Er EFAULT 261.Fa Path , 262.Fa argv , 263or 264.Fa envp 265point 266to an illegal address. 267.It Bq Er EIO 268An I/O error occurred while reading from the file system. 269.El 270.Sh CAVEAT 271If a program is 272.Em setuid 273to a non-super-user, but is executed when 274the real 275.Em uid 276is ``root'', then the program has some of the powers 277of a super-user as well. 278.Sh SEE ALSO 279.Xr ktrace 1 , 280.Xr _exit 2 , 281.Xr fork 2 , 282.Xr execl 3 , 283.Xr exit 3 , 284.Xr sysctl 3 , 285.Xr a.out 5 , 286.Xr elf 5 , 287.Xr environ 7 , 288.Xr mount 8 289.Sh HISTORY 290The 291.Fn execve 292function call appeared in 293.Bx 4.2 . 294