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 SYNOPSIS 42.Fd #include <unistd.h> 43.Ft int 44.Fn execve "const char *path" "char *const argv[]" "char *const 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.Sy execve Ap d , 71the system actually 72.Sy 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.Sy execve Ap d 81file becomes the second argument; 82otherwise, the name of the originally 83.Sy 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.Sy 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. 135(The effective group ID is the first element of the group list.) 136The real user ID, real group ID and 137other group IDs of the new process image remain the same as the calling 138process image. 139After any set-user-ID and set-group-ID processing, 140the effective user ID is recorded as the saved set-user-ID, 141and the effective group ID is recorded as the saved set-group-ID. 142These values may be used in changing the effective IDs later (see 143.Xr setuid 2 ) . 144.ne 1i 145.Pp 146The set-ID bits are not honored if the respective file system has the 147.Ar nosuid 148option enabled or if the new process file is an interpreter file. Syscall 149tracing is disabled if effective IDs are changed. 150.Pp 151The new process also inherits the following attributes from 152the calling process: 153.Pp 154.Bl -column parent_process_ID -offset indent -compact 155.It process ID Ta see Xr getpid 2 156.It parent process ID Ta see Xr getppid 2 157.It process group ID Ta see Xr getpgrp 2 158.It access groups Ta see Xr getgroups 2 159.It working directory Ta see Xr chdir 2 160.It root directory Ta see Xr chroot 2 161.It control terminal Ta see Xr termios 4 162.It resource usages Ta see Xr getrusage 2 163.It interval timers Ta see Xr getitimer 2 164.It resource limits Ta see Xr getrlimit 2 165.It file mode mask Ta see Xr umask 2 166.It signal mask Ta see Xr sigvec 2 , 167.Xr sigsetmask 2 168.El 169.Pp 170When a program is executed as a result of an 171.Fn execve 172call, it is entered as follows: 173.Bd -literal -offset indent 174main(argc, argv, envp) 175int argc; 176char **argv, **envp; 177.Ed 178.Pp 179where 180.Fa argc 181is the number of elements in 182.Fa argv 183(the ``arg count'') 184and 185.Fa argv 186points to the array of character pointers 187to the arguments themselves. 188.Sh IMPLEMENTATION NOTES 189.Pp 190In the non-threaded library 191.Fn execve 192is implemented as the 193.Va execve 194syscall. 195.Pp 196In the threaded library, the 197.Va execve 198syscall is assembled to 199.Fn _thread_sys_execve 200and 201.Fn execve 202is implemented as a function which performs user-thread 203library re-initialization and then calls 204.Fn _thread_sys_execve . 205.Sh RETURN VALUES 206As the 207.Fn execve 208function overlays the current process image 209with a new process image the successful call 210has no process to return to. 211If 212.Fn execve 213does return to the calling process an error has occurred; the 214return value will be -1 and the global variable 215.Va errno 216is set to indicate the error. 217.Sh ERRORS 218.Fn Execve 219will fail and return to the calling process if: 220.Bl -tag -width [ENAMETOOLONG] 221.It Bq Er ENOTDIR 222A component of the path prefix is not a directory. 223.It Bq Er ENAMETOOLONG 224A component of a pathname exceeded 255 characters, 225or an entire path name exceeded 1023 characters. 226.It Bq Er ENOENT 227The new process file does not exist. 228.It Bq Er ELOOP 229Too many symbolic links were encountered in translating the pathname. 230.It Bq Er EACCES 231Search permission is denied for a component of the path prefix. 232.It Bq Er EACCES 233The new process file is not an ordinary file. 234.It Bq Er EACCES 235The new process file mode denies execute permission. 236.It Bq Er ENOEXEC 237The new process file has the appropriate access 238permission, but has an invalid magic number in its header. 239.It Bq Er ETXTBSY 240The new process file is a pure procedure (shared text) 241file that is currently open for writing or reading by some process. 242.ne 1i 243.It Bq Er ENOMEM 244The new process requires more virtual memory than 245is allowed by the imposed maximum 246.Pq Xr getrlimit 2 . 247.It Bq Er E2BIG 248The number of bytes in the new process' argument list 249is larger than the system-imposed limit. 250This limit is specified by the 251.Xr sysctl 3 252MIB variable 253.Dv KERN_ARGMAX . 254.It Bq Er EFAULT 255The new process file is not as long as indicated by 256the size values in its header. 257.It Bq Er EFAULT 258.Fa Path , 259.Fa argv , 260or 261.Fa envp 262point 263to an illegal address. 264.It Bq Er EIO 265An I/O error occurred while reading from the file system. 266.El 267.Sh CAVEAT 268If a program is 269.Em setuid 270to a non-super-user, but is executed when 271the real 272.Em uid 273is ``root'', then the program has some of the powers 274of a super-user as well. 275.Sh SEE ALSO 276.Xr ktrace 1 , 277.Xr _exit 2 , 278.Xr fork 2 , 279.Xr execl 3 , 280.Xr exit 3 , 281.Xr sysctl 3 , 282.Xr environ 7 , 283.Xr mount 8 284.Sh HISTORY 285The 286.Fn execve 287function call appeared in 288.Bx 4.2 . 289