NAME
execve - 执行程序
总览 (SYNOPSIS)
#include <unistd.h>
int execve (const char *filename, char *const argv [], char *const envp[]);
描述 (DESCRIPTION)
execve() 执行 filename 指出的 程序. filename 必须 是二进制可执行文件, 或者 以 "#! interpreter [arg]" 行 开始的 脚本文件. 后者的 interpreter 必须是 某个 可执行文件 的 有效 路径, 这个 可执行文件 自身不能是 脚本程序, 调用 形式 是 "interpreter [arg] filename".
execve() 调用 成功 后 不会 返回, 其 进程 的 正文(text), 数据(data), bss 和 堆栈(stack) 段 被 调入程序 覆盖. 调入程序 继承了 调用程序 的 PID 和所有 打开的 文件描述符, 他们 不会 因为 exec 过程 而 关闭. 父进程 的 未决 信号被 清除. 所有 被 调用进程 设置过 的 信号 重置为 缺省行为.
如果 当前程序 正在 被 ptrace 跟踪, 成功的 调用 execve() 后 将 收到一个 SIGTRAP 信号.
如果 可执行文件 是 动态连接 的 a.out 二进制程序, 含有 共享库 的 stub, 开始 执行 程序 的 时候, Linux 动态 连接器(linker) ld.so(8) 把 所需的 共享库 调入 核心, 并且 和 程序 相连.
如果 可执行文件 是 动态连接 的 ELF 二进制程序, 定义在 PT_INTERP 字段 的解释器(interpreter) 调入 所需的 共享库. 连接 libc5 的 程序 的 典型 解释器 是 /lib/ld-linux.so.1, 而 连接 GNU libc2 (libc6) 的 程序 则为 /lib/ld-linux.so.2.
返回值 (RETURN VALUE)
调用成功 的 时候 execve() 不会 返回, 调用失败 时 返回 -1, 并 设置 errno 为 相应的 值.
错误 (ERRORS)
- EACCES
- 文件 或 脚本解释器 不正确.
- EACCES
- 没有 文件 或 脚本解释器 的 执行 权限.
- EACCES
- 文件系统 挂载(mount) 为 noexec.
- EPERM
- 文件系统 挂载为 nosuid, 使用者 不是 超级用户, 以及 文件 设置了 SUID 或 SGID 位.
- EPERM
- 进程 正 被跟踪, 使用者 不是 超级用户, 以及 文件 设置了 SUID 或 SGID 位.
- E2BIG
- 参数列表 过长.
- ENOEXEC
- 可执行文件 的 文件格式 无法 识别, 误用在 不同的 体系结构, 或者 其他 格式错误 导致 程序 无法 执行.
- EFAULT
- filename 指针 超出 可访问 的 地址空间.
- ENAMETOOLONG
- filename 太长.
- ENOENT
- filename , 脚本解释器, 或 ELF 解释器 不存在.
- ENOMEM
- 内核 空间 不足.
- ENOTDIR
- 在 filename , 脚本解释器 或 ELF 解释器 的 前缀 路径 中, 某些 成员 不是 目录.
- EACCES
- 在 filename 或 脚本解释器 的 前缀 路径 中, 对 某些 目录 没有 访问许可.
- ELOOP
- 解析 filename , 脚本解释器 或 ELF 解释器 时 遇到 过多的 符号连接.
- ETXTBUSY
- 可执行文件 被 一个 或 多个 进程 以 写方式 打开.
- EIO
- 发生 I/O 错误.
- ENFILE
- 达到 系统 定义的 同时打开文件数 限制.
- EMFILE
- 进程 打开了 最大数量 的 文件.
- EINVAL
- 该 ELF 可执行文件 拥有 多个 PT_INTERP 字段 (就是说, 试图 定义 多个 解释器).
- EISDIR
- ELF 解释器 是 目录.
- ELIBBAD
- 无法 识别 ELF 解释器 的 格式.
CONFORMING TO
SVr4, SVID, X/OPEN, BSD 4.3. POSIX 没有 对 #! 行为 的 文档, 但有 其他的兼容 形式. SVr4 记录了 额外的 错误情况 EAGAIN, EINTR, ELIBACC, ENOLINK, EMULTIHOP; POSIX 没有 关于 ETXTBSY, EPERM, EFAULT, ELOOP, EIO, ENFILE, EMFILE, EINVAL, EISDIR 或 ELIBBAD 错误情况 的 文档.
注意 (NOTES)
SUID and SGID processes can not be ptrace()d SUID or SGID.
在 #! 格式的 shell 可执行脚本 中, 第一行 的 长度 不得 超过 127 字节.
Linux 忽略 脚本程序 的 SUID 和 SGID 位.
另见 (SEE ALSO)
ld.so(8), execl(3), fork(2)
#p#
NAME
execve - execute program
SYNOPSIS
#include <unistd.h>
int execve(const char *filename, char *const argv [], char *const envp[]);
DESCRIPTION
execve() executes the program pointed to by filename. filename must be either a binary executable, or a script starting with a line of the form "#! interpreter [arg]". In the latter case, the interpreter must be a valid pathname for an executable which is not itself a script, which will be invoked as interpreter [arg] filename.
argv is an array of argument strings passed to the new program. envp is an array of strings, conventionally of the form key=value, which are passed as environment to the new program. Both argv and envp must be terminated by a null pointer. The argument vector and environment can be accessed by the called program's main function, when it is defined as int main(int argc, char *argv[], char *envp[]).
execve() does not return on success, and the text, data, bss, and stack of the calling process are overwritten by that of the program loaded. The program invoked inherits the calling process's PID, and any open file descriptors that are not set to close on exec. Signals pending on the calling process are cleared. Any signals set to be caught by the calling process are reset to their default behaviour. The SIGCHLD signal (when set to SIG_IGN) may or may not be reset to SIG_DFL.
If the current program is being ptraced, a SIGTRAP is sent to it after a successful execve().
If the set-uid bit is set on the program file pointed to by filename the effective user ID of the calling process is changed to that of the owner of the program file. Similarly, when the set-gid bit of the program file is set the effective group ID of the calling process is set to the group of the program file.
If the executable is an a.out dynamically-linked binary executable containing shared-library stubs, the Linux dynamic linker ld.so(8) is called at the start of execution to bring needed shared libraries into core and link the executable with them.
If the executable is a dynamically-linked ELF executable, the interpreter named in the PT_INTERP segment is used to load the needed shared libraries. This interpreter is typically /lib/ld-linux.so.1 for binaries linked with the Linux libc version 5, or /lib/ld-linux.so.2 for binaries linked with the GNU libc version 2.
RETURN VALUE
On success, execve() does not return, on error -1 is returned, and errno is set appropriately.
ERRORS
- EACCES
- The file or a script interpreter is not a regular file.
- EACCES
- Execute permission is denied for the file or a script or ELF interpreter.
- EACCES
- The file system is mounted noexec.
- EPERM
- The file system is mounted nosuid, the user is not the superuser, and the file has an SUID or SGID bit set.
- EPERM
- The process is being traced, the user is not the superuser and the file has an SUID or SGID bit set.
- E2BIG
- The argument list is too big.
- ENOEXEC
- An executable is not in a recognised format, is for the wrong architecture, or has some other format error that means it cannot be executed.
- EFAULT
- filename points outside your accessible address space.
- ENAMETOOLONG
- filename is too long.
- ENOENT
- The file filename or a script or ELF interpreter does not exist, or a shared library needed for file or interpreter cannot be found.
- ENOMEM
- Insufficient kernel memory was available.
- ENOTDIR
- A component of the path prefix of filename or a script or ELF interpreter is not a directory.
- EACCES
- Search permission is denied on a component of the path prefix of filename or the name of a script interpreter.
- ELOOP
- Too many symbolic links were encountered in resolving filename or the name of a script or ELF interpreter.
- ETXTBSY
- Executable was open for writing by one or more processes.
- EIO
- An I/O error occurred.
- ENFILE
- The limit on the total number of files open on the system has been reached.
- EMFILE
- The process has the maximum number of files open.
- EINVAL
- An ELF executable had more than one PT_INTERP segment (i.e., tried to name more than one interpreter).
- EISDIR
- An ELF interpreter was a directory.
- ELIBBAD
- An ELF interpreter was not in a recognised format.
CONFORMING TO
SVr4, SVID, X/OPEN, BSD 4.3. POSIX does not document the #! behavior but is otherwise compatible. SVr4 documents additional error conditions EAGAIN, EINTR, ELIBACC, ENOLINK, EMULTIHOP; POSIX does not document ETXTBSY, EPERM, EFAULT, ELOOP, EIO, ENFILE, EMFILE, EINVAL, EISDIR or ELIBBAD error conditions.
NOTES
SUID and SGID processes can not be ptrace()d.
Linux ignores the SUID and SGID bits on scripts.
The result of mounting a filesystem nosuid vary between Linux kernel versions: some will refuse execution of SUID/SGID executables when this would give the user powers she did not have already (and return EPERM), some will just ignore the SUID/SGID bits and exec successfully.
A maximum line length of 127 characters is allowed for the first line in a #! executable shell script.
HISTORICAL
With Unix V6 the argument list of an exec call was ended by 0, while the argument list of main was ended by -1. Thus, this argument list was not directly usable in a further exec call. Since Unix V7 both are NULL.
SEE ALSO
chmod(2), fork(2), execl(3), environ(5), ld.so(8)
