rsync stops at system call select()

[jian li]

hi, all:
       I need to back up about 50 files, the size of which won't exceed 5m,
every 10~15 minutes to four remote machines.

       The back up command is written in a shell script file and was
executed by the scheduling program with system() function. The scheduling
program is implemented with c++.
       The command as follow:
         *rsync -az  /home/admin/service/* admin at 10.249.49.101:
/news_hot_data*

      * At first, this works just fine.* But after about one or two days,
rsync will stop at some place  and the whole backup process stuck.
       The following is the output with -vv option when backup stop:
         *opening connection using: ssh -l admin 10.249.49.101 rsync
--server -vvlogDtprze.isf . /news_hot_data*

       I used strace to track the system call, and I found select() was
invoked again and again, never end until the program was killed by ctrl+c.
The following is the output:
          ......
          18477 select(1027, [255 1024], [], NULL, NULL) = 1 (in
[1024])

          18477 read(1024, "\36\0\0\0", 16384)    = 4
          18477 select(1027, [255 1024], [255], NULL, NULL) = 1 (out [255])
          18477 write(255,
"]\306\304\2315\r\346\314\26]\2\275\350|X\305X\216\361\"\301}\t\34\213\357GPS\360\214\370"...,
48) = 48
          18477 select(1027, [255 1024], [], NULL, NULL) = 1 (in [255])
          18477 read(255,
"l\210\377V\20\270\0270\276@\363N\366\n!\311\211\312\206\216\25\3\1\323\375\370\24\0174lM\312"...,
8192) = 48
          18477 select(1027, [255 1024], [1025], NULL, NULL) = 1 (out
[1025])
          18477 write(1025, "\35\0\0\0\335\226\333L", 8) = 8
          18477 select(1027, [255 1024], [], NULL, NULL <unfinished
...>
          18476 <... select resumed> )            = 0 (Timeout)
          18476 select(1026, [], [], NULL, {60, 0}) = 0 (Timeout)
          18476 select(1026, [], [], NULL, {60, 0}) = 0
(Timeout)
          18476 select(1026, [], [], NULL, {60, 0}) = 0 (Timeout)
          18476 select(1026, [], [], NULL, {60, 0}) = 0
(Timeout)
          18476 select(1026, [], [], NULL, {60, 0}) = 0 (Timeout)
          18476 select(1026, [], [], NULL, {60, 0}) = 0
(Timeout)
          18476 select(1026, [], [], NULL, {60, 0}) = 0
(Timeout)
          18476 select(1026, [], [], NULL, {60, 0}) = 0
(Timeout)
          18476 select(1026, [], [], NULL, {60, 0}) = 0
(Timeout)
          18476 select(1026, [], [], NULL, {60, 0}) = 0
(Timeout)
          18476 select(1026, [], [], NULL, {60, 0}) = 0
(Timeout)
           ......
           I read the linux manual about select(), know it was used to wait
something to be ready, but I don't know what exactly it is waiting, and it
never will ready.
           *And what made me more confused is that when I execute the script
in the terminal, it still works!*

           I have been confused for a few days and try to find out the
reason by google, but failed.


thanks
James li
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