a UNIX process has three standard file descriptors
0 == stdin
1 == stdout
2 == stderr
the 2>&1 means attach fd 2 to write to the same as stream as fd 1, essentially calling dup2()
the 2nd & means run the program in parallel, fork()/exec() but don't wait().
command >out.file 2>&1 &
command >out.file是将command的输出重定向到out.file文件,即输出内容不打印到屏幕上,而是输出到out.file文件中。 2>&1 是将标准出错重定向到标准输出,这里的标准输出已经重定向到了out.file文件,即将标准出错也输出到out.file文件中。最后一个& , 是让该命令在后台执行。