Explanation of the meaning of "2>&1″" in the Linux shell script

The script is: nohup/mnt/nand3/h2000g  >/dev/null  2>&1 &  for & 1 more accurately said file descriptor 1, and 1 The general Representative is Stdout_fileno, which is actually a dup2 (2) call. He outputs the standard output to All_result, and then copies the standard output to the file Descriptor 2 (Stderr_fileno), The consequence is that the file descriptors 1 and 2 point to the same file table entry, or the wrong output is merged. where 0 means keyboard input 1 means that the screen output 2 indicates an error output. REDIRECT standard error to standard output, then throw it under/dev/null. In layman's words, all standard output and standard errors are thrown into the trash.  # command >out.file  2>&1 & command >out.file is to redirect the command output to the Out.file file, that is, the output is not printed to the screen, but is output to the Out.file file. 2>&1 is redirecting standard errors to standard output, where the standard output has been redirected to the Out.file file, and the standard error is output to the Out.file file. The last & is to have the command execute in the background.   Imagine what 2>1 stands for, 2 and > combined for error redirection, and 1 for error redirection to a file 1 instead of standard output; replacing 2>&1,& with 1 represents standard output, which becomes error redirection to standard output.   You can use:  ls 2>1 test, will not report No 2 file errors, but will output an empty file 1;ls xxx 2>1 test, no xxx This file error output to 1; LS xxx 2>&1 test, will not generate 1 of this file, but the error ran to the standard output, ls xxx >out.txt 2>&1, actually can be replaced by ls xxx 1>out.txt 2>&1; redirect symbol > default is 1, Errors and outputs are uploaded to the out.txt.   Why 2>&1 to write in the back?  # command > File 2>&1  First is command > file redirect standard output to file, 2>&1 is the standard error copy of the standard output behavior, which is also redirected to file, the end result is that the standard output and errors are redirected to file. The  # command 2>&1 >file 2>&1 Standard error copies the behavior of the standard output, but at this point the standard output is still in the terminal. The output is redirected to file after >file, but the standard error remains at the terminal.   can be seen with Strace:  1. Command > File 2>&1 the key system call sequence that implements redirection in this order is: open (file) = = 3dup2 (3,1) dup2 ( 2). Command 2>&1 >file The key system call sequence that implements the redirect is: Dup2 () open (file) = = 3dup2 (3,1)  

Meaning of 2>&1″ in the Linux shell script