1.\" $NetBSD: execve.2,v 1.14 1998/08/29 08:32:36 lukem 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 8.5 (Berkeley) 6/1/94 35.\" 36.Dd June 1, 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.\" was .Fn execve Ap d , 72\fBexecve\fP'd, 73the system 74.\" was .Fn execve Ap s 75\fBexecve\fP's 76runs the specified 77.Em interpreter . 78If the optional 79.Em arg 80is specified, it becomes the first argument to the 81.Em interpreter , 82and the name of the originally 83.\" was .Fn execve Ap d 84\fBexecve\fP'd 85file becomes the second argument; 86otherwise, the name of the originally 87.\" was .Fn execve Ap d 88\fBexecve\fP'd 89file becomes the first argument. The original arguments are shifted over to 90become the subsequent arguments. The zeroth argument, normally the name of the 91.\" was .Fn execve Ap d 92\fBexecve\fP'd 93file, is left unchanged. 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. Signals which are set to be caught in the calling process image 127are set to default action in the new process image. 128Blocked signals remain blocked regardless of changes to the signal action. 129The signal stack is reset to be undefined (see 130.Xr sigaction 2 131for more information). 132.Pp 133If the set-user-ID mode bit of the new process image file is set 134(see 135.Xr chmod 2 ) , 136the effective user ID of the new process image is set to the owner ID 137of the new process image file. 138If the set-group-ID mode bit of the new process image file is set, 139the effective group ID of the new process image is set to the group ID 140of the new process image file. 141(The effective group ID is the first element of the group list.) 142The real user ID, real group ID and 143other group IDs of the new process image remain the same as the calling 144process image. 145After any set-user-ID and set-group-ID processing, 146the effective user ID is recorded as the saved set-user-ID, 147and the effective group ID is recorded as the saved set-group-ID. 148These values may be used in changing the effective IDs later (see 149.Xr setuid 2 ) . 150.ne 1i 151.Pp 152The new process also inherits the following attributes from 153the calling process: 154.Pp 155.Bl -column parent_process_ID -offset indent -compact 156.It process ID Ta see Xr getpid 2 157.It parent process ID Ta see Xr getppid 2 158.It process group ID Ta see Xr getpgrp 2 159.It access groups Ta see Xr getgroups 2 160.It working directory Ta see Xr chdir 2 161.It root directory Ta see Xr chroot 2 162.It control terminal Ta see Xr termios 4 163.It resource usages Ta see Xr getrusage 2 164.It interval timers Ta see Xr getitimer 2 165.It resource limits Ta see Xr getrlimit 2 166.It file mode mask Ta see Xr umask 2 167.It signal mask Ta see Xr sigaction 2 , 168.Xr sigprocmask 2 169.El 170.Pp 171When a program is executed as a result of an 172.Fn execve 173call, it is entered as follows: 174.Bd -literal -offset indent 175main(argc, argv, envp) 176int argc; 177char **argv, **envp; 178.Ed 179.Pp 180where 181.Fa argc 182is the number of elements in 183.Fa argv 184(the ``arg count'') 185and 186.Fa argv 187points to the array of character pointers 188to the arguments themselves. 189.Sh RETURN VALUES 190As the 191.Fn execve 192function overlays the current process image 193with a new process image the successful call 194has no process to return to. 195If 196.Fn execve 197does return to the calling process an error has occurred; the 198return value will be -1 and the global variable 199.Va errno 200is set to indicate the error. 201.Sh ERRORS 202.Fn execve 203will fail and return to the calling process if: 204.Bl -tag -width Er 205.It Bq Er ENOTDIR 206A component of the path prefix is not a directory. 207.It Bq Er ENAMETOOLONG 208A component of a pathname exceeded 209.Dv {NAME_MAX} 210characters, or an entire path name exceeded 211.Dv {PATH_MAX} 212characters. 213.It Bq Er ENOENT 214The new process file does not exist. 215.It Bq Er ELOOP 216Too many symbolic links were encountered in translating the pathname. 217.It Bq Er EACCES 218Search permission is denied for a component of the path prefix. 219.It Bq Er EACCES 220The new process file is not an ordinary file. 221.It Bq Er EACCES 222The new process file mode denies execute permission. 223.It Bq Er EACCES 224The new process file is on a filesystem mounted with execution 225disabled 226.Pf ( Dv MNT_NOEXEC 227in 228.Ao Pa sys/mount.h Ac ) . 229.It Bq Er ENOEXEC 230The new process file has the appropriate access 231permission, but has an invalid magic number in its header. 232.It Bq Er ETXTBSY 233The new process file is a pure procedure (shared text) 234file that is currently open for writing or reading by some process. 235.ne 1i 236.It Bq Er ENOMEM 237The new process requires more virtual memory than 238is allowed by the imposed maximum 239.Pq Xr getrlimit 2 . 240.It Bq Er E2BIG 241The number of bytes in the new process's argument list 242is larger than the system-imposed limit. 243The limit in the system as released is 20480 bytes 244.Pf ( Dv NCARGS 245in 246.Ao Pa sys/param.h Ac ) . 247.It Bq Er EFAULT 248The new process file is not as long as indicated by 249the size values in its header. 250.It Bq Er EFAULT 251.Fa path , 252.Fa argv , 253or 254.Fa envp 255point 256to an illegal address. 257.It Bq Er EIO 258An I/O error occurred while reading from the file system. 259.El 260.Sh CAVEAT 261If a program is 262.Em setuid 263to a non-super-user, but is executed when 264the real 265.Em uid 266is ``root'', then the program has some of the powers 267of a super-user as well. 268.Sh SEE ALSO 269.Xr _exit 2 , 270.Xr fork 2 , 271.Xr execl 3 , 272.Xr environ 7 273.Sh STANDARDS 274The 275.Fn execve 276function conforms to 277.St -p1003.1-90 . 278.Sh HISTORY 279The 280.Fn execve 281function call appeared in 282.Bx 4.2 . 283