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Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)execve.2 8.5 (Berkeley) 6/1/94 29.\" $FreeBSD: src/lib/libc/sys/execve.2,v 1.16.2.10 2001/12/22 01:21:30 jwd Exp $ 30.\" 31.Dd January 23, 2021 32.Dt EXECVE 2 33.Os 34.Sh NAME 35.Nm execve 36.Nd execute a file 37.Sh LIBRARY 38.Lb libc 39.Sh SYNOPSIS 40.In unistd.h 41.Ft int 42.Fn execve "const char *path" "char *const argv[]" "char *const envp[]" 43.Sh DESCRIPTION 44.Fn Execve 45transforms the calling process into a new process. 46The new process is constructed from an ordinary file, 47whose name is pointed to by 48.Fa path , 49called the 50.Em new process file . 51This file is either an executable object file, 52or a file of data for an interpreter. 53An executable object file consists of an identifying header, 54followed by pages of data representing the initial program (text) 55and initialized data pages. 56Additional pages may be specified 57by the header to be initialized with zero data; see 58.Xr elf 5 59and 60.Xr a.out 5 . 61.Pp 62An interpreter file begins with a line of the form: 63.Pp 64.Bd -ragged -offset indent -compact 65.Sy \&#! 66.Em interpreter 67.Bq Em arg 68.Ed 69.Pp 70When an interpreter file is 71.Sy execve Ap d , 72the system actually 73.Sy execve Ap s 74the specified 75.Em interpreter . 76If the optional 77.Em arg 78is specified, it becomes the first argument to the 79.Em interpreter , 80and the name of the originally 81.Sy execve Ap d 82file becomes the second argument; 83otherwise, the name of the originally 84.Sy execve Ap d 85file becomes the first argument. 86The original arguments are shifted over to become the subsequent arguments. 87The zeroth argument is set to the specified 88.Em interpreter . 89(See 90.Xr script 7 91for a detailed discussion of interpreter file execution.) 92.Pp 93The argument 94.Fa argv 95is a pointer to a null-terminated array of 96character pointers to null-terminated character strings. 97These strings construct the argument list to be made available to the new 98process. 99At least one argument must be present in 100the array; by custom, the first element should be 101the name of the executed program (for example, the last component of 102.Fa path ) . 103.Pp 104The argument 105.Fa envp 106is also a pointer to a null-terminated array of 107character pointers to null-terminated strings. 108A pointer to this array is normally stored in the global variable 109.Va environ . 110These strings pass information to the 111new process that is not directly an argument to the command (see 112.Xr environ 7 ) . 113.Pp 114File descriptors open in the calling process image remain open in 115the new process image, except for those for which the close-on-exec 116flag is set (see 117.Xr close 2 118and 119.Xr fcntl 2 ) . 120Descriptors that remain open are unaffected by 121.Fn execve . 122If any of the standard descriptors (0, 1, and/or 2) are closed at the time 123.Fn execve 124is called, and the process will gain privilege as a result of set-id 125semantics, those descriptors will be reopened automatically. 126No programs, whether privileged or not, should assume that these descriptors 127will remain closed across a call to 128.Fn execve . 129.Pp 130Signals set to be ignored in the calling process are set to be ignored in 131the 132new process. 133Signals which are set to be caught in the calling process image 134are set to default action in the new process image. 135Blocked signals remain blocked regardless of changes to the signal action. 136The signal stack is reset to be undefined (see 137.Xr sigaction 2 138for more information). 139.Pp 140If the set-user-ID mode bit of the new process image file is set 141(see 142.Xr chmod 2 ) , 143the effective user ID of the new process image is set to the owner ID 144of the new process image file. 145If the set-group-ID mode bit of the new process image file is set, 146the effective group ID of the new process image is set to the group ID 147of the new process image file. 148(The effective group ID is the first element of the group list.) 149The real user ID, real group ID and 150other group IDs of the new process image remain the same as the calling 151process image. 152After any set-user-ID and set-group-ID processing, 153the effective user ID is recorded as the saved set-user-ID, 154and the effective group ID is recorded as the saved set-group-ID. 155These values may be used in changing the effective IDs later (see 156.Xr setuid 2 ) . 157.Pp 158The set-ID bits are not honored if the respective file system has the 159.Ar nosuid 160option enabled or if the new process file is an interpreter file. 161Syscall tracing is disabled if effective IDs are changed. 162.Pp 163The new process also inherits the following attributes from 164the calling process: 165.Pp 166.Bl -column parent_process_ID -offset indent -compact 167.It process ID Ta see Xr getpid 2 168.It parent process ID Ta see Xr getppid 2 169.It process group ID Ta see Xr getpgrp 2 170.It access groups Ta see Xr getgroups 2 171.It working directory Ta see Xr chdir 2 172.It root directory Ta see Xr chroot 2 173.It control terminal Ta see Xr termios 4 174.It resource usages Ta see Xr getrusage 2 175.It interval timers Ta see Xr getitimer 2 176.It resource limits Ta see Xr getrlimit 2 177.It file mode mask Ta see Xr umask 2 178.It signal mask Ta see Xr sigaction 2 , 179.Xr sigprocmask 2 180.El 181.Pp 182When a program is executed as a result of an 183.Fn execve 184call, it is entered as follows: 185.Bd -literal -offset indent 186.Fn main "int argc" "char **argv" "char **envp" ; 187.Ed 188.Pp 189where 190.Fa argc 191is the number of elements in 192.Fa argv 193(the 194.Dq argument count ) 195and 196.Fa argv 197points to the array of character pointers 198to the arguments themselves. 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 Er 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 ENAMETOOLONG 221When invoking an interpreted script, the interpreter name 222exceeds 223.Dv MAXSHELLCMDLEN 224characters. 225.It Bq Er ENOENT 226The new process file does not exist. 227.It Bq Er ELOOP 228Too many symbolic links were encountered in translating the pathname. 229.It Bq Er EACCES 230Search permission is denied for a component of the path prefix. 231.It Bq Er EACCES 232The new process file is not an ordinary file. 233.It Bq Er EACCES 234The new process file mode denies execute permission. 235.It Bq Er ENOEXEC 236The new process file has the appropriate access 237permission, but has an invalid magic number in its header. 238.It Bq Er ETXTBSY 239The new process file is a pure procedure (shared text) 240file that is currently open for writing or reading by some process. 241.It Bq Er ENOMEM 242The new process requires more virtual memory than 243is allowed by the imposed maximum 244.Pq Xr getrlimit 2 . 245.It Bq Er E2BIG 246The number of bytes in the new process' argument list 247is larger than the system-imposed limit. 248This limit is specified by the 249.Xr sysctl 3 250MIB variable 251.Dv KERN_ARGMAX . 252.It Bq Er EFAULT 253The new process file is not as long as indicated by 254the size values in its header. 255.It Bq Er EFAULT 256.Fa Path , 257.Fa argv , 258or 259.Fa envp 260point 261to an illegal address. 262.It Bq Er EIO 263An I/O error occurred while reading from the file system. 264.El 265.Sh CAVEATS 266If a program is 267.Em setuid 268to a non-super-user, but is executed when 269the real 270.Em uid 271is 272.Dq root , 273then the program has some of the powers 274of a super-user as well. 275.Sh SEE ALSO 276.Xr ktrace 1 , 277.Xr _exit 2 , 278.Xr fork 2 , 279.Xr execl 3 , 280.Xr exit 3 , 281.Xr sysctl 3 , 282.Xr a.out 5 , 283.Xr elf 5 , 284.Xr environ 7 , 285.Xr script 7 , 286.Xr mount 8 287.Sh STANDARDS 288The 289.Fn execve 290system call conforms to 291.St -p1003.1-2004 . 292.Pp 293The support for executing interpreted programs is an extension. 294.Sh HISTORY 295The 296.Fn execve 297function call appeared in 298.Bx 4.2 . 299