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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.\" 34.Dd June 1, 1994 35.Dt EXECVE 2 36.Os BSD 4 37.Sh NAME 38.Nm execve 39.Nd execute a file 40.Sh SYNOPSIS 41.Fd #include <unistd.h> 42.Ft int 43.Fn execve "const char *path" "char *const argv[]" "char *const envp[]" 44.Sh DESCRIPTION 45.Fn Execve 46transforms the calling process into a new process. 47The new process is constructed from an ordinary file, 48whose name is pointed to by 49.Fa path , 50called the 51.Em new process file . 52This file is either an executable object file, 53or a file of data for an interpreter. 54An executable object file consists of an identifying header, 55followed by pages of data representing the initial program (text) 56and initialized data pages. Additional pages may be specified 57by the header to be initialized with zero data; see 58.Xr a.out 5 . 59.Pp 60An interpreter file begins with a line of the form: 61.Pp 62.Bd -filled -offset indent -compact 63.Sy \&#! 64.Em interpreter 65.Bq Em arg 66.Ed 67.Pp 68When an interpreter file is 69.Sy execve Ap d , 70the system 71.Sy execve Ap s 72runs the specified 73.Em interpreter . 74If the optional 75.Em arg 76is specified, it becomes the first argument to the 77.Em interpreter , 78and the name of the originally 79.Sy execve Ap d 80file becomes the second argument; 81otherwise, the name of the originally 82.Sy execve Ap d 83file becomes the first argument. The original arguments are shifted over to 84become the subsequent arguments. The zeroth argument, normally the name of the 85.Sy execve Ap d 86file, is left unchanged. 87.Pp 88The argument 89.Fa argv 90is a pointer to a null-terminated array of 91character pointers to null-terminated character strings. 92These strings construct the argument list to be made available to the new 93process. At least one argument must be present in 94the array; by custom, the first element should be 95the name of the executed program (for example, the last component of 96.Fa path ) . 97.Pp 98The argument 99.Fa envp 100is also a pointer to a null-terminated array of 101character pointers to null-terminated strings. 102A pointer to this array is normally stored in the global variable 103.Va environ. 104These strings pass information to the 105new process that is not directly an argument to the command (see 106.Xr environ 7 ) . 107.Pp 108File descriptors open in the calling process image remain open in 109the new process image, except for those for which the close-on-exec 110flag is set (see 111.Xr close 2 112and 113.Xr fcntl 2 ) . 114Descriptors that remain open are unaffected by 115.Fn execve . 116.Pp 117Signals set to be ignored in the calling process are set to be ignored in 118the 119new process. Signals which are set to be caught in the calling process image 120are set to default action in the new process image. 121Blocked signals remain blocked regardless of changes to the signal action. 122The signal stack is reset to be undefined (see 123.Xr sigaction 2 124for more information). 125.Pp 126If the set-user-ID mode bit of the new process image file is set 127(see 128.Xr chmod 2 ) , 129the effective user ID of the new process image is set to the owner ID 130of the new process image file. 131If the set-group-ID mode bit of the new process image file is set, 132the effective group ID of the new process image is set to the group ID 133of the new process image file. 134(The effective group ID is the first element of the group list.) 135The real user ID, real group ID and 136other group IDs of the new process image remain the same as the calling 137process image. 138After any set-user-ID and set-group-ID processing, 139the effective user ID is recorded as the saved set-user-ID, 140and the effective group ID is recorded as the saved set-group-ID. 141These values may be used in changing the effective IDs later (see 142.Xr setuid 2 ) . 143.ne 1i 144.Pp 145The new process also inherits the following attributes from 146the calling process: 147.Pp 148.Bl -column parent_process_ID -offset indent -compact 149.It process ID Ta see Xr getpid 2 150.It parent process ID Ta see Xr getppid 2 151.It process group ID Ta see Xr getpgrp 2 152.It access groups Ta see Xr getgroups 2 153.It working directory Ta see Xr chdir 2 154.It root directory Ta see Xr chroot 2 155.It control terminal Ta see Xr termios 4 156.It resource usages Ta see Xr getrusage 2 157.It interval timers Ta see Xr getitimer 2 158.It resource limits Ta see Xr getrlimit 2 159.It file mode mask Ta see Xr umask 2 160.It signal mask Ta see Xr sigvec 2 , 161.Xr sigsetmask 2 162.El 163.Pp 164When a program is executed as a result of an 165.Fn execve 166call, it is entered as follows: 167.Bd -literal -offset indent 168main(argc, argv, envp) 169int argc; 170char **argv, **envp; 171.Ed 172.Pp 173where 174.Fa argc 175is the number of elements in 176.Fa argv 177(the ``arg count'') 178and 179.Fa argv 180points to the array of character pointers 181to the arguments themselves. 182.Sh IMPLEMENTATION NOTES 183.Pp 184In the non-threaded library 185.Fn execve 186is implemented as the 187.Va execve 188syscall. 189.Pp 190In the threaded library, the 191.Va execve 192syscall is assembled to 193.Fn _thread_sys_execve 194and 195.Fn execve 196is implemented as a function which performs user-thread 197library re-initialization and then calls 198.Fn _thread_sys_execve . 199.Sh RETURN VALUES 200As the 201.Fn execve 202function overlays the current process image 203with a new process image the successful call 204has no process to return to. 205If 206.Fn execve 207does return to the calling process an error has occurred; the 208return value will be -1 and the global variable 209.Va errno 210is set to indicate the error. 211.Sh ERRORS 212.Fn Execve 213will fail and return to the calling process if: 214.Bl -tag -width [ENAMETOOLONG] 215.It Bq Er ENOTDIR 216A component of the path prefix is not a directory. 217.It Bq Er ENAMETOOLONG 218A component of a pathname exceeded 255 characters, 219or an entire path name exceeded 1023 characters. 220.It Bq Er ENOENT 221The new process file does not exist. 222.It Bq Er ELOOP 223Too many symbolic links were encountered in translating the pathname. 224.It Bq Er EACCES 225Search permission is denied for a component of the path prefix. 226.It Bq Er EACCES 227The new process file is not an ordinary file. 228.It Bq Er EACCES 229The new process file mode denies execute permission. 230.It Bq Er ENOEXEC 231The new process file has the appropriate access 232permission, but has an invalid magic number in its header. 233.It Bq Er ETXTBSY 234The new process file is a pure procedure (shared text) 235file that is currently open for writing or reading by some process. 236.ne 1i 237.It Bq Er ENOMEM 238The new process requires more virtual memory than 239is allowed by the imposed maximum 240.Pq Xr getrlimit 2 . 241.It Bq Er E2BIG 242The number of bytes in the new process's argument list 243is larger than the system-imposed limit. 244The limit in the system as released is 65536 bytes 245.Pf ( Dv NCARGS 246in 247.Ao Pa sys/param.h Ac ) . 248.It Bq Er EFAULT 249The new process file is not as long as indicated by 250the size values in its header. 251.It Bq Er EFAULT 252.Fa Path , 253.Fa argv , 254or 255.Fa envp 256point 257to an illegal address. 258.It Bq Er EIO 259An I/O error occurred while reading from the file system. 260.El 261.Sh CAVEAT 262If a program is 263.Em setuid 264to a non-super-user, but is executed when 265the real 266.Em uid 267is ``root'', then the program has some of the powers 268of a super-user as well. 269.Sh SEE ALSO 270.Xr _exit 2 , 271.Xr fork 2 , 272.Xr execl 3 , 273.Xr exit 3 , 274.Xr environ 7 275.Sh HISTORY 276The 277.Fn execve 278function call appeared in 279.Bx 4.2 . 280