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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: src/lib/libc/sys/execve.2,v 1.16.2.10 2001/12/22 01:21:30 jwd Exp $ 34.\" $DragonFly: src/lib/libc/sys/execve.2,v 1.3 2007/12/21 22:14:04 swildner Exp $ 35.\" 36.Dd December 21, 2007 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.In unistd.h 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 elf 5 63and 64.Xr a.out 5 . 65.Pp 66An interpreter file begins with a line of the form: 67.Pp 68.Bd -ragged -offset indent -compact 69.Sy \&#! 70.Em interpreter 71.Bq Em arg 72.Ed 73.Pp 74When an interpreter file is 75.Sy execve Ap d , 76the system actually 77.Sy execve Ap s 78the 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.Sy execve Ap d 86file becomes the second argument; 87otherwise, the name of the originally 88.Sy execve Ap d 89file becomes the first argument. The original arguments are shifted over to 90become the subsequent arguments. 91The zeroth argument is set to the specified 92.Em interpreter . 93(See 94.Xr script 7 95for a detailed discussion of interpreter file execution.) 96.Pp 97The argument 98.Fa argv 99is a pointer to a null-terminated array of 100character pointers to null-terminated character strings. 101These strings construct the argument list to be made available to the new 102process. At least one argument must be present in 103the array; by custom, the first element should be 104the name of the executed program (for example, the last component of 105.Fa path ) . 106.Pp 107The argument 108.Fa envp 109is also a pointer to a null-terminated array of 110character pointers to null-terminated strings. 111A pointer to this array is normally stored in the global variable 112.Va environ . 113These strings pass information to the 114new process that is not directly an argument to the command (see 115.Xr environ 7 ) . 116.Pp 117File descriptors open in the calling process image remain open in 118the new process image, except for those for which the close-on-exec 119flag is set (see 120.Xr close 2 121and 122.Xr fcntl 2 ) . 123Descriptors that remain open are unaffected by 124.Fn execve . 125.Pp 126Signals set to be ignored in the calling process are set to be ignored in 127the 128new process. 129Signals which are set to be caught in the calling process image 130are set to default action in the new process image. 131Blocked signals remain blocked regardless of changes to the signal action. 132The signal stack is reset to be undefined (see 133.Xr sigaction 2 134for more information). 135.Pp 136If the set-user-ID mode bit of the new process image file is set 137(see 138.Xr chmod 2 ) , 139the effective user ID of the new process image is set to the owner ID 140of the new process image file. 141If the set-group-ID mode bit of the new process image file is set, 142the effective group ID of the new process image is set to the group ID 143of the new process image file. 144(The effective group ID is the first element of the group list.) 145The real user ID, real group ID and 146other group IDs of the new process image remain the same as the calling 147process image. 148After any set-user-ID and set-group-ID processing, 149the effective user ID is recorded as the saved set-user-ID, 150and the effective group ID is recorded as the saved set-group-ID. 151These values may be used in changing the effective IDs later (see 152.Xr setuid 2 ) . 153.Pp 154The set-ID bits are not honored if the respective file system has the 155.Ar nosuid 156option enabled or if the new process file is an interpreter file. Syscall 157tracing is disabled if effective IDs are changed. 158.Pp 159The new process also inherits the following attributes from 160the calling process: 161.Pp 162.Bl -column parent_process_ID -offset indent -compact 163.It process ID Ta see Xr getpid 2 164.It parent process ID Ta see Xr getppid 2 165.It process group ID Ta see Xr getpgrp 2 166.It access groups Ta see Xr getgroups 2 167.It working directory Ta see Xr chdir 2 168.It root directory Ta see Xr chroot 2 169.It control terminal Ta see Xr termios 4 170.It resource usages Ta see Xr getrusage 2 171.It interval timers Ta see Xr getitimer 2 172.It resource limits Ta see Xr getrlimit 2 173.It file mode mask Ta see Xr umask 2 174.It signal mask Ta see Xr sigvec 2 , 175.Xr sigsetmask 2 176.El 177.Pp 178When a program is executed as a result of an 179.Fn execve 180call, it is entered as follows: 181.Bd -literal -offset indent 182main(argc, argv, envp) 183int argc; 184char **argv, **envp; 185.Ed 186.Pp 187where 188.Fa argc 189is the number of elements in 190.Fa argv 191(the ``arg count'') 192and 193.Fa argv 194points to the array of character pointers 195to the arguments themselves. 196.Sh RETURN VALUES 197As the 198.Fn execve 199function overlays the current process image 200with a new process image the successful call 201has no process to return to. 202If 203.Fn execve 204does return to the calling process an error has occurred; the 205return value will be -1 and the global variable 206.Va errno 207is set to indicate the error. 208.Sh ERRORS 209.Fn Execve 210will fail and return to the calling process if: 211.Bl -tag -width Er 212.It Bq Er ENOTDIR 213A component of the path prefix is not a directory. 214.It Bq Er ENAMETOOLONG 215A component of a pathname exceeded 255 characters, 216or an entire path name exceeded 1023 characters. 217.It Bq Er ENAMETOOLONG 218When invoking an interpreted script, the interpreter name 219exceeds 220.Dv MAXSHELLCMDLEN 221characters. 222.It Bq Er ENOENT 223The new process file does not exist. 224.It Bq Er ELOOP 225Too many symbolic links were encountered in translating the pathname. 226.It Bq Er EACCES 227Search permission is denied for a component of the path prefix. 228.It Bq Er EACCES 229The new process file is not an ordinary file. 230.It Bq Er EACCES 231The new process file mode denies execute permission. 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.It Bq Er ENOMEM 239The new process requires more virtual memory than 240is allowed by the imposed maximum 241.Pq Xr getrlimit 2 . 242.It Bq Er E2BIG 243The number of bytes in the new process' argument list 244is larger than the system-imposed limit. 245This limit is specified by the 246.Xr sysctl 3 247MIB variable 248.Dv KERN_ARGMAX . 249.It Bq Er EFAULT 250The new process file is not as long as indicated by 251the size values in its header. 252.It Bq Er EFAULT 253.Fa Path , 254.Fa argv , 255or 256.Fa envp 257point 258to an illegal address. 259.It Bq Er EIO 260An I/O error occurred while reading from the file system. 261.El 262.Sh CAVEAT 263If a program is 264.Em setuid 265to a non-super-user, but is executed when 266the real 267.Em uid 268is ``root'', then the program has some of the powers 269of a super-user as well. 270.Sh SEE ALSO 271.Xr ktrace 1 , 272.Xr fork 2 , 273.Xr _exit 2 , 274.Xr execl 3 , 275.Xr exit 3 , 276.Xr sysctl 3 , 277.Xr a.out 5 , 278.Xr elf 5 , 279.Xr environ 7 , 280.Xr script 7 , 281.Xr mount 8 282.Sh HISTORY 283The 284.Fn execve 285function call appeared in 286.Bx 4.2 . 287