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 . 123If any of the standard descriptors (0, 1, and/or 2) are closed at the 124time 125.Fn execve 126is called, and the process will gain privilege as a result of set-id 127semantics, those descriptors will be re-opened automatically. 128No programs, whether privileged or not, should assume that these descriptors 129will remain closed across a call to 130.Fn execve . 131.Pp 132Signals set to be ignored in the calling process are set to be ignored in 133the 134new process. 135Signals which are set to be caught in the calling process image 136are set to default action in the new process image. 137Blocked signals remain blocked regardless of changes to the signal action. 138The signal stack is reset to be undefined (see 139.Xr sigaction 2 140for more information). 141.Pp 142If the set-user-ID mode bit of the new process image file is set 143(see 144.Xr chmod 2 ) , 145the effective user ID of the new process image is set to the owner ID 146of the new process image file. 147If the set-group-ID mode bit of the new process image file is set, 148the effective group ID of the new process image is set to the group ID 149of the new process image file. 150(The effective group ID is the first element of the group list.) 151The real user ID, real group ID and 152other group IDs of the new process image remain the same as the calling 153process image. 154After any set-user-ID and set-group-ID processing, 155the effective user ID is recorded as the saved set-user-ID, 156and the effective group ID is recorded as the saved set-group-ID. 157These values may be used in changing the effective IDs later (see 158.Xr setuid 2 ) . 159.Pp 160The set-ID bits are not honored if the respective file system has the 161.Ar nosuid 162option enabled or if the new process file is an interpreter file. Syscall 163tracing is disabled if effective IDs are changed. 164.Pp 165The new process also inherits the following attributes from 166the calling process: 167.Pp 168.Bl -column parent_process_ID -offset indent -compact 169.It process ID Ta see Xr getpid 2 170.It parent process ID Ta see Xr getppid 2 171.It process group ID Ta see Xr getpgrp 2 172.It access groups Ta see Xr getgroups 2 173.It working directory Ta see Xr chdir 2 174.It root directory Ta see Xr chroot 2 175.It control terminal Ta see Xr termios 4 176.It resource usages Ta see Xr getrusage 2 177.It interval timers Ta see Xr getitimer 2 178.It resource limits Ta see Xr getrlimit 2 179.It file mode mask Ta see Xr umask 2 180.It signal mask Ta see Xr sigvec 2 , 181.Xr sigsetmask 2 182.El 183.Pp 184When a program is executed as a result of an 185.Fn execve 186call, it is entered as follows: 187.Bd -literal -offset indent 188main(argc, argv, envp) 189int argc; 190char **argv, **envp; 191.Ed 192.Pp 193where 194.Fa argc 195is the number of elements in 196.Fa argv 197(the ``arg count'') 198and 199.Fa argv 200points to the array of character pointers 201to the arguments themselves. 202.Sh RETURN VALUES 203As the 204.Fn execve 205function overlays the current process image 206with a new process image the successful call 207has no process to return to. 208If 209.Fn execve 210does return to the calling process an error has occurred; the 211return value will be -1 and the global variable 212.Va errno 213is set to indicate the error. 214.Sh ERRORS 215The 216.Fn execve 217function 218will fail and return to the calling process if: 219.Bl -tag -width Er 220.It Bq Er ENOTDIR 221A component of the path prefix is not a directory. 222.It Bq Er ENAMETOOLONG 223A component of a pathname exceeded 255 characters, 224or an entire path name exceeded 1023 characters. 225.It Bq Er ENAMETOOLONG 226When invoking an interpreted script, the interpreter name 227exceeds 228.Dv MAXSHELLCMDLEN 229characters. 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 fork 2 , 281.Xr _exit 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 STANDARDS 290The 291.Fn execve 292function conforms to 293.St -p1003.1-2001 , 294with the exception of reopening descriptors 0, 1, and/or 2 in certain 295circumstances. 296A future update of the Standard is expected to require this behavior, 297and it may become the default for non-privileged processes as well. 298.\" NB: update this caveat when TC1 is blessed. 299The support for executing interpreted programs is an extension. 300.Sh HISTORY 301The 302.Fn execve 303function call appeared in 304.Bx 4.2 . 305