The close-on-exec flag (FD_CLOEXEC ; see fcntl (2)) for the duplicate descriptor is off. dup2 () The dup2 () system call performs the same task as dup (), but instead of using the lowest-numbered unused file descriptor, it uses the descriptor number specified in newfd.

dup2니까 뭔가 더 발전된 시스템콜이라고 보여질 수 있겠네요. 하지만 dup과 dup2의 사용 용도는 완벽하게 다릅니다. 1.dup2 - 파일 식별자를 복제한다. #include //man page 참조. int dup2 ( int old_fd1 , int new_fd2 ); 똑같이 파일 식별자를 복제한다고 되어있지만, 매개변수로 생각해 볼 수 있는 전개는. old_fd1을 new_fd2로 바꿔버린다! 인데,

EINTR The dup2() or dup3() call was interrupted by a signal; … On some systems, dup2() also sometimes returns EINVAL like F_DUPFD. If newfd was open, any errors that would have been reported at close(2) time are lost. If this is of concern, then—unless the program is single-threaded and does not allocate file descriptors in signal handlers—the correct approach is not to close newfd before calling dup2 (), because of the race condition described above. 2018-09-08 (Linux only) This may be returned by dup2() or dup3() during a race condition with open(2) and dup(). EINTR The dup2 () or dup3 () call was interrupted by a signal; see signal(7) . dup2()¶ The dup2() system call performs the same task as dup(), but instead of using the lowest-numbered unused file descriptor, it uses the file descriptor number specified in newfd.

EINTR The dup2() or dup3() call was interrupted by a signal; see signal(7). EINVAL (dup3()) flags contain an invalid value. EINVAL (dup3()) oldfd was equal to newfd. EMFILE The dup () and dup2 () functions provide an alternative interface to the service provided by fcntl () using the F_DUPFD command.

The dup2 () function is not intended for use in critical regions as a synchronization mechanism. dup () and dup2 () create a copy of the file descriptor oldfd.

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EINTR The dup2 () or dup3 () call was interrupted by a signal; see signal (7). The dup () and dup2 () functions provide an alternative interface to the service provided by fcntl () using the F_DUPFD command. The dup2() function is not marked obsolescent because it presents a type-safe version of functionality provided in a type-unsafe version by fcntl(). It is used in the POSIX Ada binding.

DUP Section: Linux Programmer's Manual (2) Updated: 2017-09-15 Index NAME dup, dup2, dup3 - duplicate a file descriptor SYNOPSIS #include int dup(int oldfd); int dup2(int oldfd, int newfd); #define _GNU_SOURCE /* See feature_test_macros(7) / #include / Obtain O_* constant definitions */ #include int dup3(int oldfd, int newfd, int flags);

#include int dup(int fildes); int dup2(int fildes, int fildes2); Description dup2() makes newfd be the copy of oldfd, closing newfd first if necessary, but note the following: If oldfd is not a valid file descriptor, then the call fails, and newfd is not closed. If oldfd is a valid file descriptor, and newfd has the same value as oldfd , then dup2 () does nothing, and returns newfd .

Ou oldfd était égal à newfd. EMFILE Introduction In the presentation Fire & Ice: Making and Breaking macOS Firewalls, Patrick Wardle mentioned the idea of using binaries signed by Apple to by-pass firewall checks for outbound traffic. Linux笔记（5）| 文件IO操作(续) dup并不能指定分配的新的文件描述符的数字，dup2系统调用修复了这个缺陷，所以平时项目中实际使用时根据具体情况来决定用dup还是dup2.dup2复制的文件描述fd中0、1、2已经默认被系统占用了，因此用户进程得到的最小的fd就是3了。 Compile: “gcc -fno-stack-protector -z execstack linux_x86_bind.c -o linux_x86_bind” Running it we can see it’s waiting for incoming connections, we use netcat to connect to our machine. Because the bind shell is listening on all IP addresses we simply use the loopback address, and port 1234: These one-liners are all found on pentestmonkey.net.This website also contains a bunch of other useful stuff!
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EINTR . A signal was caught during the dup2() system call.

若参数newfd为一已打开的文件描述词, 则newfd 所指的文件会先被关闭. dup2()所复制的文件描述词, 与原来的文件描述词共享各种文件状态, 详情可参考dup().
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Understanding fork() and dup2() is the other half. Let’s see how these functions work! Running Commands in a Pipeline. In the diagrams we’ve seen so far, pipes were used when passing data from one command’s process to another, but we haven’t discussed the hierarchy of processes that run such commands.

Loyola College > Department of Computer Science > Dr. James Glenn > CS 702 > Examples and Lecture Notes > Using dup2 for I/O Redirection and Pipes. redirect.c DUP Section: Linux Programmer's Manual (2) Updated: 2017-09-15 Index NAME dup, dup2, dup3 - duplicate a file descriptor SYNOPSIS #include int dup(int oldfd); int dup2(int oldfd, int newfd); #define _GNU_SOURCE /* See feature_test_macros(7) */ #include /* Obtain O_* constant definitions */ #include int dup3(int oldfd, int newfd, int flags); (Linux only) This may be returned by dup2() or dup3() during a race condition with open(2) and dup(). EINTR The dup2 () or dup3 () call was interrupted by a signal; see signal (7).

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Understanding fork() and dup2() is the other half. Let’s see how these functions work! Running Commands in a Pipeline. In the diagrams we’ve seen so far, pipes were used when passing data from one command’s process to another, but we haven’t discussed the hierarchy of processes that run such commands.

EINTR: The dup2() call was interrupted by a signal. EMFILE: The process already has the maximum number of file descriptors open and tried to open a new one. EBADF oldfd isn't an open file descriptor, or newfd is out of the allowed range for file descriptors. EBUSY (Linux only) This may be returned by dup2() or dup3() during a race condition with open(2) and dup().