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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 186main(argc, argv, envp) 187int argc; 188char **argv, **envp; 189.Ed 190.Pp 191where 192.Fa argc 193is the number of elements in 194.Fa argv 195(the ``arg count'') 196and 197.Fa argv 198points to the array of character pointers 199to the arguments themselves. 200.Sh RETURN VALUES 201As the 202.Fn execve 203function overlays the current process image 204with a new process image the successful call 205has no process to return to. 206If 207.Fn execve 208does return to the calling process an error has occurred; the 209return value will be -1 and the global variable 210.Va errno 211is set to indicate the error. 212.Sh ERRORS 213.Fn Execve 214will fail and return to the calling process if: 215.Bl -tag -width Er 216.It Bq Er ENOTDIR 217A component of the path prefix is not a directory. 218.It Bq Er ENAMETOOLONG 219A component of a pathname exceeded 255 characters, 220or an entire path name exceeded 1023 characters. 221.It Bq Er ENAMETOOLONG 222When invoking an interpreted script, the interpreter name 223exceeds 224.Dv MAXSHELLCMDLEN 225characters. 226.It Bq Er ENOENT 227The new process file does not exist. 228.It Bq Er ELOOP 229Too many symbolic links were encountered in translating the pathname. 230.It Bq Er EACCES 231Search permission is denied for a component of the path prefix. 232.It Bq Er EACCES 233The new process file is not an ordinary file. 234.It Bq Er EACCES 235The new process file mode denies execute permission. 236.It Bq Er ENOEXEC 237The new process file has the appropriate access 238permission, but has an invalid magic number in its header. 239.It Bq Er ETXTBSY 240The new process file is a pure procedure (shared text) 241file that is currently open for writing or reading by some process. 242.It Bq Er ENOMEM 243The new process requires more virtual memory than 244is allowed by the imposed maximum 245.Pq Xr getrlimit 2 . 246.It Bq Er E2BIG 247The number of bytes in the new process' argument list 248is larger than the system-imposed limit. 249This limit is specified by the 250.Xr sysctl 3 251MIB variable 252.Dv KERN_ARGMAX . 253.It Bq Er EFAULT 254The new process file is not as long as indicated by 255the size values in its header. 256.It Bq Er EFAULT 257.Fa Path , 258.Fa argv , 259or 260.Fa envp 261point 262to an illegal address. 263.It Bq Er EIO 264An I/O error occurred while reading from the file system. 265.El 266.Sh CAVEATS 267If a program is 268.Em setuid 269to a non-super-user, but is executed when 270the real 271.Em uid 272is ``root'', then the program has some of the powers 273of a super-user as well. 274.Sh SEE ALSO 275.Xr ktrace 1 , 276.Xr _exit 2 , 277.Xr fork 2 , 278.Xr execl 3 , 279.Xr exit 3 , 280.Xr sysctl 3 , 281.Xr a.out 5 , 282.Xr elf 5 , 283.Xr environ 7 , 284.Xr script 7 , 285.Xr mount 8 286.Sh STANDARDS 287The 288.Fn execve 289system call conforms to 290.St -p1003.1-2004 . 291.Pp 292The support for executing interpreted programs is an extension. 293.Sh HISTORY 294The 295.Fn execve 296function call appeared in 297.Bx 4.2 . 298