1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.man% 5.\" 6.\" @(#)execve.2 8.5 (Berkeley) 06/01/94 7.\" 8.Dd 9.Dt EXECVE 2 10.Os BSD 4 11.Sh NAME 12.Nm execve 13.Nd execute a file 14.Sh SYNOPSIS 15.Fd #include <unistd.h> 16.Ft int 17.Fn execve "const char *path" "char *const argv[]" "char *const envp[]" 18.Sh DESCRIPTION 19.Fn Execve 20transforms the calling process into a new process. 21The new process is constructed from an ordinary file, 22whose name is pointed to by 23.Fa path , 24called the 25.Em new process file . 26This file is either an executable object file, 27or a file of data for an interpreter. 28An executable object file consists of an identifying header, 29followed by pages of data representing the initial program (text) 30and initialized data pages. Additional pages may be specified 31by the header to be initialized with zero data; see 32.Xr a.out 5 . 33.Pp 34An interpreter file begins with a line of the form: 35.Pp 36.Bd -filled -offset indent -compact 37.Sy \&#! 38.Em interpreter 39.Bq Em arg 40.Ed 41.Pp 42When an interpreter file is 43.\" was .Fn execve Ap d , 44\fBexecve\fP'd, 45the system 46.\" was .Fn execve Ap s 47\fBexecve\fP's 48runs the specified 49.Em interpreter . 50If the optional 51.Em arg 52is specified, it becomes the first argument to the 53.Em interpreter , 54and the name of the originally 55.\" was .Fn execve Ap d 56\fBexecve\fP'd 57file becomes the second argument; 58otherwise, the name of the originally 59.\" was .Fn execve Ap d 60\fBexecve\fP'd 61file becomes the first argument. The original arguments are shifted over to 62become the subsequent arguments. The zeroth argument, normally the name of the 63.\" was .Fn execve Ap d 64\fBexecve\fP'd 65file, is left unchanged. 66.Pp 67The argument 68.Fa argv 69is a pointer to a null-terminated array of 70character pointers to null-terminated character strings. 71These strings construct the argument list to be made available to the new 72process. At least one argument must be present in 73the array; by custom, the first element should be 74the name of the executed program (for example, the last component of 75.Fa path ) . 76.Pp 77The argument 78.Fa envp 79is also a pointer to a null-terminated array of 80character pointers to null-terminated strings. 81A pointer to this array is normally stored in the global variable 82.Va environ. 83These strings pass information to the 84new process that is not directly an argument to the command (see 85.Xr environ 7 ) . 86.Pp 87File descriptors open in the calling process image remain open in 88the new process image, except for those for which the close-on-exec 89flag is set (see 90.Xr close 2 91and 92.Xr fcntl 2 ) . 93Descriptors that remain open are unaffected by 94.Fn execve . 95.Pp 96Signals set to be ignored in the calling process are set to be ignored in 97the 98new process. Signals which are set to be caught in the calling process image 99are set to default action in the new process image. 100Blocked signals remain blocked regardless of changes to the signal action. 101The signal stack is reset to be undefined (see 102.Xr sigaction 2 103for more information). 104.Pp 105If the set-user-ID mode bit of the new process image file is set 106(see 107.Xr chmod 2 ) , 108the effective user ID of the new process image is set to the owner ID 109of the new process image file. 110If the set-group-ID mode bit of the new process image file is set, 111the effective group ID of the new process image is set to the group ID 112of the new process image file. 113(The effective group ID is the first element of the group list.) 114The real user ID, real group ID and 115other group IDs of the new process image remain the same as the calling 116process image. 117After any set-user-ID and set-group-ID processing, 118the effective user ID is recorded as the saved set-user-ID, 119and the effective group ID is recorded as the saved set-group-ID. 120These values may be used in changing the effective IDs later (see 121.Xr setuid 2 ) . 122.ne 1i 123.Pp 124The new process also inherits the following attributes from 125the calling process: 126.Pp 127.Bl -column parent_process_ID -offset indent -compact 128.It process ID Ta see Xr getpid 2 129.It parent process ID Ta see Xr getppid 2 130.It process group ID Ta see Xr getpgrp 2 131.It access groups Ta see Xr getgroups 2 132.It working directory Ta see Xr chdir 2 133.It root directory Ta see Xr chroot 2 134.It control terminal Ta see Xr termios 4 135.It resource usages Ta see Xr getrusage 2 136.It interval timers Ta see Xr getitimer 2 137.It resource limits Ta see Xr getrlimit 2 138.It file mode mask Ta see Xr umask 2 139.It signal mask Ta see Xr sigvec 2 , 140.Xr sigsetmask 2 141.El 142.Pp 143When a program is executed as a result of an 144.Fn execve 145call, it is entered as follows: 146.Bd -literal -offset indent 147main(argc, argv, envp) 148int argc; 149char **argv, **envp; 150.Ed 151.Pp 152where 153.Fa argc 154is the number of elements in 155.Fa argv 156(the ``arg count'') 157and 158.Fa argv 159points to the array of character pointers 160to the arguments themselves. 161.Sh RETURN VALUES 162As the 163.Fn execve 164function overlays the current process image 165with a new process image the successful call 166has no process to return to. 167If 168.Fn execve 169does return to the calling process an error has occurred; the 170return value will be -1 and the global variable 171.Va errno 172is set to indicate the error. 173.Sh ERRORS 174.Fn Execve 175will fail and return to the calling process if: 176.Bl -tag -width [ENAMETOOLONG] 177.It Bq Er ENOTDIR 178A component of the path prefix is not a directory. 179.It Bq Er EINVAL 180The pathname contains a character with the high-order bit set. 181.It Bq Er ENAMETOOLONG 182A component of a pathname exceeded 255 characters, 183or an entire path name exceeded 1023 characters. 184.It Bq Er ENOENT 185The new process file does not exist. 186.It Bq Er ELOOP 187Too many symbolic links were encountered in translating the pathname. 188.It Bq Er EACCES 189Search permission is denied for a component of the path prefix. 190.It Bq Er EACCES 191The new process file is not an ordinary file. 192.It Bq Er EACCES 193The new process file mode denies execute permission. 194.It Bq Er ENOEXEC 195The new process file has the appropriate access 196permission, but has an invalid magic number in its header. 197.It Bq Er ETXTBSY 198The new process file is a pure procedure (shared text) 199file that is currently open for writing or reading by some process. 200.ne 1i 201.It Bq Er ENOMEM 202The new process requires more virtual memory than 203is allowed by the imposed maximum 204.Pq Xr getrlimit 2 . 205.It Bq Er E2BIG 206The number of bytes in the new process's argument list 207is larger than the system-imposed limit. 208The limit in the system as released is 20480 bytes 209.Pf ( Dv NCARGS 210in 211.Ao Pa sys/param.h Ac . 212.It Bq Er EFAULT 213The new process file is not as long as indicated by 214the size values in its header. 215.It Bq Er EFAULT 216.Fa Path , 217.Fa argv , 218or 219.Fa envp 220point 221to an illegal address. 222.It Bq Er EIO 223An I/O error occurred while reading from the file system. 224.El 225.Sh CAVEAT 226If a program is 227.Em setuid 228to a non-super-user, but is executed when 229the real 230.Em uid 231is ``root'', then the program has some of the powers 232of a super-user as well. 233.Sh SEE ALSO 234.Xr exit 2 , 235.Xr fork 2 , 236.Xr execl 3 , 237.Xr environ 7 238.Sh HISTORY 239The 240.Nm 241function call appeared in 242.Bx 4.2 . 243