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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.\" $FreeBSD$ 34.\" 35.Dd June 1, 1994 36.Dt EXECVE 2 37.Os BSD 4 38.Sh NAME 39.Nm execve 40.Nd execute a file 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.Fd #include <unistd.h> 45.Ft int 46.Fn execve "const char *path" "char *const argv[]" "char *const envp[]" 47.Sh DESCRIPTION 48.Fn Execve 49transforms the calling process into a new process. 50The new process is constructed from an ordinary file, 51whose name is pointed to by 52.Fa path , 53called the 54.Em new process file . 55This file is either an executable object file, 56or a file of data for an interpreter. 57An executable object file consists of an identifying header, 58followed by pages of data representing the initial program (text) 59and initialized data pages. Additional pages may be specified 60by the header to be initialized with zero data; see 61.Xr a.out 5 . 62.Pp 63An interpreter file begins with a line of the form: 64.Pp 65.Bd -filled -offset indent -compact 66.Sy \&#! 67.Em interpreter 68.Bq Em arg 69.Ed 70.Pp 71When an interpreter file is 72.Sy execve Ap d , 73the system actually 74.Sy execve Ap s 75the specified 76.Em interpreter . 77If the optional 78.Em arg 79is specified, it becomes the first argument to the 80.Em interpreter , 81and the name of the originally 82.Sy execve Ap d 83file becomes the second argument; 84otherwise, the name of the originally 85.Sy execve Ap d 86file becomes the first argument. The original arguments are shifted over to 87become the subsequent arguments. 88The zeroth argument is set to the specified 89.Em interpreter . 90.Pp 91The argument 92.Fa argv 93is a pointer to a null-terminated array of 94character pointers to null-terminated character strings. 95These strings construct the argument list to be made available to the new 96process. At least one argument must be present in 97the array; by custom, the first element should be 98the name of the executed program (for example, the last component of 99.Fa path ) . 100.Pp 101The argument 102.Fa envp 103is also a pointer to a null-terminated array of 104character pointers to null-terminated strings. 105A pointer to this array is normally stored in the global variable 106.Va environ. 107These strings pass information to the 108new process that is not directly an argument to the command (see 109.Xr environ 7 ) . 110.Pp 111File descriptors open in the calling process image remain open in 112the new process image, except for those for which the close-on-exec 113flag is set (see 114.Xr close 2 115and 116.Xr fcntl 2 ) . 117Descriptors that remain open are unaffected by 118.Fn execve . 119.Pp 120Signals set to be ignored in the calling process are set to be ignored in 121the 122new process. 123Signals which are set to be caught in the calling process image 124are set to default action in the new process image. 125Blocked signals remain blocked regardless of changes to the signal action. 126The signal stack is reset to be undefined (see 127.Xr sigaction 2 128for more information). 129.Pp 130If the set-user-ID mode bit of the new process image file is set 131(see 132.Xr chmod 2 ) , 133the effective user ID of the new process image is set to the owner ID 134of the new process image file. 135If the set-group-ID mode bit of the new process image file is set, 136the effective group ID of the new process image is set to the group ID 137of the new process image file. 138(The effective group ID is the first element of the group list.) 139The real user ID, real group ID and 140other group IDs of the new process image remain the same as the calling 141process image. 142After any set-user-ID and set-group-ID processing, 143the effective user ID is recorded as the saved set-user-ID, 144and the effective group ID is recorded as the saved set-group-ID. 145These values may be used in changing the effective IDs later (see 146.Xr setuid 2 ) . 147.ne 1i 148.Pp 149The set-ID bits are not honored if the respective file system has the 150.Ar nosuid 151option enabled or if the new process file is an interpreter file. Syscall 152tracing is disabled if effective IDs are changed. 153.Pp 154The new process also inherits the following attributes from 155the calling process: 156.Pp 157.Bl -column parent_process_ID -offset indent -compact 158.It process ID Ta see Xr getpid 2 159.It parent process ID Ta see Xr getppid 2 160.It process group ID Ta see Xr getpgrp 2 161.It access groups Ta see Xr getgroups 2 162.It working directory Ta see Xr chdir 2 163.It root directory Ta see Xr chroot 2 164.It control terminal Ta see Xr termios 4 165.It resource usages Ta see Xr getrusage 2 166.It interval timers Ta see Xr getitimer 2 167.It resource limits Ta see Xr getrlimit 2 168.It file mode mask Ta see Xr umask 2 169.It signal mask Ta see Xr sigvec 2 , 170.Xr sigsetmask 2 171.El 172.Pp 173When a program is executed as a result of an 174.Fn execve 175call, it is entered as follows: 176.Bd -literal -offset indent 177main(argc, argv, envp) 178int argc; 179char **argv, **envp; 180.Ed 181.Pp 182where 183.Fa argc 184is the number of elements in 185.Fa argv 186(the ``arg count'') 187and 188.Fa argv 189points to the array of character pointers 190to the arguments themselves. 191.Sh IMPLEMENTATION NOTES 192.Pp 193In the non-threaded library 194.Fn execve 195is implemented as the 196.Va execve 197syscall. 198.Pp 199In the threaded library, the 200.Va execve 201syscall is assembled to 202.Fn _thread_sys_execve 203and 204.Fn execve 205is implemented as a function which performs user-thread 206library re-initialization and then calls 207.Fn _thread_sys_execve . 208.Sh RETURN VALUES 209As the 210.Fn execve 211function overlays the current process image 212with a new process image the successful call 213has no process to return to. 214If 215.Fn execve 216does return to the calling process an error has occurred; the 217return value will be -1 and the global variable 218.Va errno 219is set to indicate the error. 220.Sh ERRORS 221.Fn Execve 222will fail and return to the calling process if: 223.Bl -tag -width Er 224.It Bq Er ENOTDIR 225A component of the path prefix is not a directory. 226.It Bq Er ENAMETOOLONG 227A component of a pathname exceeded 255 characters, 228or an entire path name exceeded 1023 characters. 229.It Bq Er ENOENT 230The new process file does not exist. 231.It Bq Er ELOOP 232Too many symbolic links were encountered in translating the pathname. 233.It Bq Er EACCES 234Search permission is denied for a component of the path prefix. 235.It Bq Er EACCES 236The new process file is not an ordinary file. 237.It Bq Er EACCES 238The new process file mode denies execute permission. 239.It Bq Er ENOEXEC 240The new process file has the appropriate access 241permission, but has an invalid magic number in its header. 242.It Bq Er ETXTBSY 243The new process file is a pure procedure (shared text) 244file that is currently open for writing or reading by some process. 245.ne 1i 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 _exit 2 , 281.Xr fork 2 , 282.Xr execl 3 , 283.Xr exit 3 , 284.Xr sysctl 3 , 285.Xr environ 7 , 286.Xr mount 8 287.Sh HISTORY 288The 289.Fn execve 290function call appeared in 291.Bx 4.2 . 292