プロセスでファイルディスクリプタを書き込むときにファイルディスクリプタを開き、端末にエコーする方法
引数で指定されたファイル記述子にログを書き込むバックアッププログラムDuplicityがあります--log-fd=16。
もちろん、実行するとlsof -p <duplicity PID>以下が表示されます。
python2 9224 myuser 0r CHR 1,3 0t0 6 /dev/null
python2 9224 myuser 1w CHR 1,3 0t0 6 /dev/null
python2 9224 myuser 2w CHR 1,3 0t0 6 /dev/null
python2 9224 myuser 3u a_inode 0,11 0 7005 [eventfd]
python2 9224 myuser 4u unix 0x0000000000000000 0t0 158199 type=STREAM
python2 9224 myuser 5u a_inode 0,11 0 7005 [eventfd]
python2 9224 myuser 6u a_inode 0,11 0 7005 [eventfd]
python2 9224 myuser 7r DIR 8,3 4096 22414346 <some random file being accessed during the backup>
python2 9224 myuser 8r CHR 1,9 0t0 11 /dev/urandom
python2 9224 myuser 15r FIFO 0,10 0t0 157054 pipe
python2 9224 myuser 16w FIFO 0,10 0t0 157054 pipe
ただし、Pythonでファイル記述子を開こうとすると、次のエラーが発生します。
>>> import os
>>> os.fdopen(16)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
OSError: [Errno 9] Bad file descriptor
なぜこれですか？ファイル記述子を読む方法は？
ベストアンサー1
使用法strace(システムコールとシグナルトラッキング)
使用法:
sudo strace -p <PID of writing process> -s 9999 -e write=<corresponding FD>
マニュアルページから：
-p pid Attach to the process with the process ID pid and begin tracing. The trace may be terminated
at any time by a keyboard interrupt signal (CTRL-C). strace will respond by detaching itself
from the traced process(es) leaving it (them) to continue running. Multiple -p options can
be used to attach to many processes in addition to command (which is optional if at least one
-p option is given). -p "`pidof PROG`" syntax is supported.
-s strsize Specify the maximum string size to print (the default is 32). Note that filenames are not
considered strings and are always printed in full.
-e read=set
Perform a full hexadecimal and ASCII dump of all the data read from file descriptors listed in the
specified set. For example, to see all input activity on file descriptors 3 and 5 use
-e read=3,5. Note that this is independent from the normal tracing of the read(2) system call
which is controlled by the option -e trace=read.
-e write=set
Perform a full hexadecimal and ASCII dump of all the data written to file descriptors listed in
the specified set. For example, to see all output activity on file descriptors 3 and 5 use
-e write=3,5. Note that this is independent from the normal tracing of the write(2) system call
which is controlled by the option -e trace=write.