进程A打开多个fds。现在，进程B想知道进程A打开的所有fds的打开标志？进程B应该使用哪些系统调用来在Linux环境中获取此信息？
答案 0 :(得分：1)
请参阅man proc，如果您知道某个流程的pid，则可以从/proc/<pid>/fdinfo
"/proc/[pid]/fdinfo/ (since kernel 2.6.22)
This is a subdirectory containing one entry for each file which the process has open, named by its file descriptor. The contents of each file can be read to obtain informa‐
tion about the corresponding file descriptor, for example:
$ cat /proc/12015/fdinfo/4
pos: 1000
flags: 01002002
The pos field is a decimal number showing the current file offset. The flags field is an octal number that displays the file access mode and file status flags (see open(2)).
The files in this directory are readable only by the owner of the process.
"
接下来可以从lsof命令获取此信息：
$ lsof +fg
COMMAND PID TID USER FD TYPE FILE-FLAG DEVICE SIZE/OFF NODE NAME
init 1816 test 13w REG W,AP,ND,NFLK,LG,0x80000 8,3 1438 10354712 /home/test/.cache/upstart/unity-panel-service.log
init 1816 test 14w REG W,AP,ND,NFLK,LG,0x80000 8,3 2004 10360543 /home/test/.cache/upstart/indicator-messages.log.1 (deleted)
init 1816 test 15u CHR RW,ND,LG,0x80000 5,2 0t0 9237 /dev/ptmx
init 1816 test 16w REG W,AP,ND,NFLK,LG,0x80000 8,3 269 10360135 /home/test/.cache/upstart/indicator-printers.log.1 (deleted)
init 1816 test 17u CHR RW,ND,LG,0x80000 5,2 0t0 9237 /dev/ptmx
init 1816 test 18w REG W,AP,ND,NFLK,LG,0x80000 8,3 4563 10354713 /home/test/.cache/upstart/dbus.log
init 1816 test 19w REG W,AP,ND,NFLK,LG,0x80000 8,3 783 10355626 /home/test/.cache/upstart/at-spi2-registryd.log.1 (deleted)
init 1816 test 20u unix RW,ND,0x80000 0x0000000000000000 0t0 16408 @/com/ubuntu/upstart-session/1000/1816
init 1816 test 21u CHR RW,ND,LG,0x80000 5,2 0t0 9237 /dev/ptmx
init 1816 test 22u unix RW,ND,0x80000 0x0000000000000000 0t0 15455 @/com/ubuntu/upstart-session/1000/1816
init 1816 test 23w REG W,AP,ND,NFLK,LG,0x80000 8,3 8715 10354691 /home/test/.cache/upstart/gnome-session-Unity.log