1.\" $NetBSD: execve.2,v 1.22 2002/02/08 01:28:17 ross 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 39.Sh NAME 40.Nm execve 41.Nd execute a file 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.Fd #include \*[Lt]unistd.h\*[Gt] 46.Ft int 47.Fn execve "const char *path" "char *const argv[]" "char *const envp[]" 48.Sh DESCRIPTION 49.Fn execve 50transforms the calling process into a new process. 51The new process is constructed from an ordinary file, 52whose name is pointed to by 53.Fa path , 54called the 55.Em new process file . 56This file is either an executable object file, 57or a file of data for an interpreter. 58An executable object file consists of an identifying header, 59followed by pages of data representing the initial program (text) 60and initialized data pages. Additional pages may be specified 61by the header to be initialized with zero data; see 62.Xr a.out 5 . 63.Pp 64An interpreter file begins with a line of the form: 65.Pp 66.Bd -filled -offset indent -compact 67.Sy \&#! 68.Em interpreter 69.Bq Em arg 70.Ed 71.Pp 72When an interpreter file is 73.\" was .Fn execve Ap d , 74\fBexecve\fP'd, 75the system 76.\" was .Fn execve Ap s 77\fBexecve\fP's 78runs the specified 79.Em interpreter . 80If the optional 81.Em arg 82is specified, it becomes the first argument to the 83.Em interpreter , 84and the name of the originally 85.\" was .Fn execve Ap d 86\fBexecve\fP'd 87file becomes the second argument; 88otherwise, the name of the originally 89.\" was .Fn execve Ap d 90\fBexecve\fP'd 91file becomes the first argument. The original arguments are shifted over to 92become the subsequent arguments. The zeroth argument, normally the name of the 93.\" was .Fn execve Ap d 94\fBexecve\fP'd 95file, is left unchanged. 96The interpreter named by 97.Em interpreter 98must not itself be an interpreter file. 99.Pp 100The argument 101.Fa argv 102is a pointer to a null-terminated array of 103character pointers to null-terminated character strings. 104These strings construct the argument list to be made available to the new 105process. At least one argument must be present in 106the array; by custom, the first element should be 107the name of the executed program (for example, the last component of 108.Fa path ) . 109.Pp 110The argument 111.Fa envp 112is also a pointer to a null-terminated array of 113character pointers to null-terminated strings. 114A pointer to this array is normally stored in the global variable 115.Va environ . 116These strings pass information to the 117new process that is not directly an argument to the command (see 118.Xr environ 7 ) . 119.Pp 120File descriptors open in the calling process image remain open in 121the new process image, except for those for which the close-on-exec 122flag is set (see 123.Xr close 2 124and 125.Xr fcntl 2 ) . 126Descriptors that remain open are unaffected by 127.Fn execve . 128.Pp 129Signals set to be ignored in the calling process are set to be ignored in 130the 131new process. Signals which are set to be caught in the calling process image 132are set to default action in the new process image. 133Blocked signals remain blocked regardless of changes to the signal action. 134The signal stack is reset to be undefined (see 135.Xr sigaction 2 136for more information). 137.Pp 138If the set-user-ID mode bit of the new process image file is set 139(see 140.Xr chmod 2 ) , 141the effective user ID of the new process image is set to the owner ID 142of the new process image file. 143If the set-group-ID mode bit of the new process image file is set, 144the effective group ID of the new process image is set to the group ID 145of the new process image file. 146(The effective group ID is the first element of the group list.) 147The real user ID, real group ID and 148other group IDs of the new process image remain the same as the calling 149process image. 150After any set-user-ID and set-group-ID processing, 151the effective user ID is recorded as the saved set-user-ID, 152and the effective group ID is recorded as the saved set-group-ID. 153These values may be used in changing the effective IDs later (see 154.Xr setuid 2 ) . 155.ne 1i 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 sigaction 2 , 173.Xr sigprocmask 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 190.Dq arg count ) 191and 192.Fa argv 193points to the array of character pointers 194to the arguments themselves. 195.Sh RETURN VALUES 196As the 197.Fn execve 198function overlays the current process image 199with a new process image the successful call 200has no process to return to. 201If 202.Fn execve 203does return to the calling process an error has occurred; the 204return value will be -1 and the global variable 205.Va errno 206is set to indicate the error. 207.Sh ERRORS 208.Fn execve 209will fail and return to the calling process if: 210.Bl -tag -width Er 211.It Bq Er ENOTDIR 212A component of the path prefix is not a directory. 213.It Bq Er ENAMETOOLONG 214A component of a pathname exceeded 215.Dv {NAME_MAX} 216characters, or an entire path name exceeded 217.Dv {PATH_MAX} 218characters. 219.It Bq Er ENOENT 220The new process file does not exist. 221.It Bq Er ELOOP 222Too many symbolic links were encountered in translating the pathname. 223.It Bq Er EACCES 224Search permission is denied for a component of the path prefix, 225the new process file is not an ordinary file, 226it's file mode denies execute permission, or 227it is on a filesystem mounted with execution 228disabled 229.Pf ( Dv MNT_NOEXEC 230in 231.Ao Pa sys/mount.h Ac ) . 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.ne 1i 239.It Bq Er ENOMEM 240The new process requires more virtual memory than 241is allowed by the imposed maximum 242.Pq Xr getrlimit 2 . 243.It Bq Er E2BIG 244The number of bytes in the new process's argument list 245is larger than the system-imposed limit. 246The limit in the system as released is 262144 bytes 247.Pf ( Dv NCARGS 248in 249.Ao Pa sys/param.h Ac ) . 250.It Bq Er EFAULT 251The new process file is not as long as indicated by 252the size values in its header. 253.It Bq Er EFAULT 254.Fa path , 255.Fa argv , 256or 257.Fa envp 258point 259to an illegal address. 260.It Bq Er EIO 261An I/O error occurred while reading from the file system. 262.El 263.Sh SEE ALSO 264.Xr _exit 2 , 265.Xr fork 2 , 266.Xr execl 3 , 267.Xr environ 7 268.Sh STANDARDS 269The 270.Fn execve 271function conforms to 272.St -p1003.1-90 . 273.Sh HISTORY 274The 275.Fn execve 276function call appeared in 277.Bx 4.2 . 278.Sh BUGS 279If a program is 280.Em setuid 281to a non-super-user, but is executed when 282the real 283.Em uid 284is 285.Dq root , 286then the program has some of the powers of a super-user as well. 287