BackupPC using rsync fails with "protocol version mismatch -- is your shell clean?"

Francisco López
2016-02-16T01:13:59Z

Hello,

I just installed BackupPC in a Debian box to use it as backup server. As
you know, this software makes use, among others, of rsync. When using the
rsync option, it fails.

Server:
Debian Jessie.
BackupPC 3.3.1 built from source, executed by user "backup-user".
Rsync 3.1.2 built from source with the default options.

Client
Debian Jessie.
Rsync 3.1.2 built from source with the default options.

After the fail, the rsync command used can be found in BackupPC's logs.
Trying the command in a shell, logged as the BackupPC user, I run into this
"protocol version mismatch -- is your shell clean?" error. The command
is:

/usr/bin/ssh -q -x -l backup-user 192.168.10.20 /usr/local/bin/rsync
--server --sender --numeric-ids --perms --owner --group -D --links
--hard-links --times --block-size=2048 --recursive --ignore-times .
/home/backup-user/test

Adding some verbose to the rsync command sent to the client, it says:

FILE_STRUCT_LEN=24, EXTRA_LEN=4

(Server) Protocol versions: remote=168430090, negotiated=31
########################### Notice the remote protocol version
protocol version mismatch -- is your shell clean?
(see the rsync man page for an explanation)
[sender] _exit_cleanup(code=2, file=compat.c, line=178): entered
rsync error: protocol incompatibility (code 2) at compat.c(178)
[sender=3.1.2]
[sender] _exit_cleanup(code=2, file=compat.c, line=178): about to call
exit(2)

In the client, using the debug script I found in this site:

/usr/bin/ssh -q -x -l backup-user 192.168.206.103
/home/backup-user/rsync-debug --server --sender --numeric-ids --perms
--owner --group -D --links --hard-links --times --block-size=2048
--recursive --ignore-times . /home/backup-user/test

rsync-2991.out content:

2997  00:58:30 brk(0)                   = 0xefb000
2997  00:58:30 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such
file
or directory)
2997  00:58:30 mmap(NULL, 8192, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fefc7341000
2997  00:58:30 access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such
file
or directory)
2997  00:58:30 open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
2997  00:58:30 fstat(3, {st_mode=S_IFREG|0644, st_size=33837, ...}) = 0
2997  00:58:30 mmap(NULL, 33837, PROT_READ, MAP_PRIVATE, 3, 0) 0x7fefc7338000
2997  00:58:30 close(3)                 = 0
2997  00:58:30 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such
file
or directory)
2997  00:58:30 open("/lib/x86_64-linux-gnu/libc.so.6",
O_RDONLY|O_CLOEXEC)
= 3
2997  00:58:30 read(3,
"\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P\34\2\0\0\0\0\0@
\0\0\0\0\0\0\0\300T\32\0\0\0\0\0\0\0\0\0@\0008\0\n\0@
\0D\0C\0\6\0\0\0\5\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0000\2\0\0\0\0\0\0000\2\0\0\0\0\0\0\10\0\0\0\0\0\0\0\3\0\0\0\4\0\0\0000\303\26\0\0\0\0\0000\303\26\0\0\0\0\0000\303\26\0\0\0\0\0\34\0\0\0\0\0\0\0\34\0\0\0\0\0\0\0\20\0\0\0\0\0\0\0\1\0\0\0\5\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\364\352\31\0\0\0\0\0\364\352\31\0\0\0\0\0\0\0
\0\0\0\0\0\1\0\0\0\6\0\0\0@\367\31\0\0\0\0\0@\3679\0\0\0\0\0@\3679\0\0\0\0\0\370O\0\0\0\0\0\0\340\222\0\0\0\0\0\0\0\0
\0\0\0\0\0\2\0\0\0\6\0\0\0\240 \32\0\0\0\0\0\240 :\0\0\0\0\0\240
:\0\0\0\0\0\340\1\0\0\0\0\0\0\340\1\0\0\0\0\0\0\10\0\0\0\0\0\0\0\4\0\0\0\4\0\0\0p\2\0\0\0\0\0\0p\2\0\0\0\0\0\0p\2\0\0\0\0\0\0D\0\0\0\0\0\0\0D\0\0\0\0\0\0\0\4\0\0\0\0\0\0\0\7\0\0\0\4\0\0\0@
\367\31\0\0\0\0\0@\3679\0\0\0\0\0@
\3679\0\0\0\0\0\20\0\0\0\0\0\0\0\200\0\0\0\0\0\0\0\10\0\0\0\0\0\0\0P\345td\4\0\0\0L\303\26\0\0\0\0\0L\303\26\0\0\0\0\0L\303\26\0\0\0\0\0$j\0\0\0\0\0\0$j\0\0\0\0\0\0\4\0\0\0\0\0\0\0Q\345td\6\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\20\0\0\0\0\0\0\0R\345td\4\0\0\0@
\367\31\0\0\0\0\0@\3679\0\0\0\0\0@
\3679\0\0\0\0\0\3008\0\0\0\0\0\0\3008\0\0\0\0\0\0\1\0\0\0\0\0\0\0\4\0\0\0\24\0\0\0\3\0\0\0GNU\0\371?y\343\344|\332K|C=\2\323!\316@\34J\205\1\4\0\0\0\20\0\0\0\1\0\0\0GNU\0\0\0\0\0\2\0\0\0\6\0\0\0
\0\0\0\0\0\0\0\363\3\0\0\n\0\0\0\0\1\0\0\16\0\0\0\0000\20D\240
\2\1\210\3\346\220\305E\214\0\300\0\10\0\5\200\0`\300\200\0\r\212\f\0\4\20\0\210D2\10.@\210P4,
\16\"H&\204\300\214\4\10\0\2\2\16\241\254\32\4f\300\0\3002\0\300\0P\1
\201\10\204\v  ($\0\4 P\0\20X\200\312DB(\0\6\200\20\30B\0
@\200\0\tP\0Q\212@\20\0\0\0\0\10\0\0\21\20",
832) = 832
2997  00:58:30 fstat(3, {st_mode=S_IFREG|0755, st_size=1729984, ...}) = 0
2997  00:58:30 mmap(NULL, 3836448, PROT_READ|PROT_EXEC,
MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fefc6d7a000
2997  00:58:30 mprotect(0x7fefc6f19000, 2097152, PROT_NONE) = 0
2997  00:58:30 mmap(0x7fefc7119000, 24576, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x19f000) = 0x7fefc7119000
2997  00:58:30 mmap(0x7fefc711f000, 14880, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fefc711f000
2997  00:58:30 close(3)                 = 0
2997  00:58:30 mmap(NULL, 4096, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fefc7337000
2997  00:58:30 mmap(NULL, 4096, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fefc7336000
2997  00:58:30 mmap(NULL, 4096, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fefc7335000
2997  00:58:30 arch_prctl(ARCH_SET_FS, 0x7fefc7336700) = 0
2997  00:58:30 mprotect(0x7fefc7119000, 16384, PROT_READ) = 0
2997  00:58:30 mprotect(0x7fefc7343000, 4096, PROT_READ) = 0
2997  00:58:30 munmap(0x7fefc7338000, 33837) = 0
2997  00:58:30 rt_sigaction(SIGUSR1, {0x41c690, [],
SA_RESTORER|SA_NOCLDSTOP, 0x7fefc6daf180}, NULL, 8) = 0
2997  00:58:30 rt_sigaction(SIGUSR2, {0x41d220, [],
SA_RESTORER|SA_NOCLDSTOP, 0x7fefc6daf180}, NULL, 8) = 0
2997  00:58:30 rt_sigaction(SIGCHLD, {0x41c630, [],
SA_RESTORER|SA_NOCLDSTOP, 0x7fefc6daf180}, NULL, 8) = 0
2997  00:58:30 geteuid()                = 1001
2997  00:58:30 getegid()                = 1001
2997  00:58:30 umask(0)                 = 022
2997  00:58:30 umask(022)               = 0
2997  00:58:30 brk(0)                   = 0xefb000
2997  00:58:30 brk(0xf1c000)            = 0xf1c000
2997  00:58:30 open("/usr/lib/locale/locale-archive",
O_RDONLY|O_CLOEXEC) 3
2997  00:58:30 fstat(3, {st_mode=S_IFREG|0644, st_size=1607632, ...}) = 0
2997  00:58:30 mmap(NULL, 1607632, PROT_READ, MAP_PRIVATE, 3, 0) 0x7fefc71ac000
2997  00:58:30 close(3)                 = 0
2997  00:58:30 open("/etc/popt", O_RDONLY) = -1 ENOENT (No such file
or
directory)
2997  00:58:30 open("/home/backup-user/.popt", O_RDONLY) = -1 ENOENT
(No
such file or directory)
2997  00:58:30 rt_sigaction(SIGINT, {0x40cca0, [],
SA_RESTORER|SA_NOCLDSTOP, 0x7fefc6daf180}, NULL, 8) = 0
2997  00:58:30 rt_sigaction(SIGHUP, {0x40cca0, [],
SA_RESTORER|SA_NOCLDSTOP, 0x7fefc6daf180}, NULL, 8) = 0
2997  00:58:30 rt_sigaction(SIGTERM, {0x40cca0, [],
SA_RESTORER|SA_NOCLDSTOP, 0x7fefc6daf180}, NULL, 8) = 0
2997  00:58:30 rt_sigprocmask(SIG_UNBLOCK, [HUP INT USR1 USR2 TERM CHLD],
NULL, 8) = 0
2997  00:58:30 rt_sigaction(SIGPIPE, {SIG_IGN, [],
SA_RESTORER|SA_NOCLDSTOP, 0x7fefc6daf180}, NULL, 8) = 0
2997  00:58:30 rt_sigaction(SIGXFSZ, {SIG_IGN, [],
SA_RESTORER|SA_NOCLDSTOP, 0x7fefc6daf180}, NULL, 8) = 0
2997  00:58:30 getcwd("/home/backup-user", 4095) = 13
2997  00:58:30 fcntl(0, F_GETFL)        = 0 (flags O_RDONLY)
2997  00:58:30 fcntl(0, F_SETFL, O_RDONLY|O_NONBLOCK) = 0
2997  00:58:30 fcntl(1, F_GETFL)        = 0x1 (flags O_WRONLY)
2997  00:58:30 fcntl(1, F_SETFL, O_WRONLY|O_NONBLOCK) = 0
2997  00:58:30 fcntl(0, F_GETFL)        = 0x800 (flags O_RDONLY|O_NONBLOCK)
2997  00:58:30 fcntl(1, F_GETFL)        = 0x801 (flags O_WRONLY|O_NONBLOCK)
2997  00:58:30 write(1, "\37\0\0\0", 4) = 4
#################################### Here is where the script stops
#############
############################# I have to hit return several times in the
server ########
2997  00:58:30 select(1, [0], NULL, [0], {60, 0}) = 1 (in [0], left {55,
558348})
2997  00:58:34 read(0, "\n", 4)         = 1
2997  00:58:34 select(1, [0], NULL, [0], {60, 0}) = 1 (in [0], left {59,
793510})
2997  00:58:35 read(0, "\n", 3)         = 1
2997  00:58:35 select(1, [0], NULL, [0], {60, 0}) = 1 (in [0], left {59,
975726})
2997  00:58:35 read(0, "\n", 2)         = 1
2997  00:58:35 select(1, [0], NULL, [0], {60, 0}) = 1 (in [0], left {59,
968630})
2997  00:58:35 read(0, "\n", 1)         = 1
2997  00:58:35 write(2, "protocol version mismatch -- is your shell
clean?", 49) = 49
2997  00:58:35 write(2, "\n", 1)        = 1
2997  00:58:35 write(2, "(see the rsync man page for an explanation)",
43)
= 43
2997  00:58:35 write(2, "\n", 1)        = 1
2997  00:58:35 rt_sigaction(SIGUSR1, {SIG_IGN, [], SA_RESTORER,
0x7fefc6daf180}, NULL, 8) = 0
2997  00:58:35 rt_sigaction(SIGUSR2, {SIG_IGN, [], SA_RESTORER,
0x7fefc6daf180}, NULL, 8) = 0
2997  00:58:35 write(2, "rsync error: protocol incompatibility (code 2) at
compat.c(178) [sender=3.1.2]", 78) = 78
2997  00:58:35 write(2, "\n", 1)        = 1
2997  00:58:35 nanosleep({0, 100000000}, NULL) = 0
2997  00:58:35 exit_group(2)            = ?
2997  00:58:35     exited with 2

After some hours of research, I can't figure out what is wrong. I removed
and checked everything that could write any text (ssh welcome message,
.bashrc echos, passphrase and even the system prompt) and rsync is still
unable to gather the files. ssh connection is made passwordless.

Looks like the 168430090 in the remote protocol is the decimal
representation for 0xA0A0A0A, but no clue of what is writing it. I searched
for similar errors in the list, but all I found are due to things I already
checked.

The lines:
2997  00:58:30 open("/etc/popt", O_RDONLY) = -1 ENOENT (No such file
or
directory)
2997  00:58:30 open("/home/backup-user/.popt", O_RDONLY) = -1 ENOENT
(No
such file or directory)

Looks suspicious to me, but also checked the libraries involved.

Options --server and --sender are added by BackupPC, but are not supposed
to be needed in a regular use, as the rsync documentation states.

Hope this information is clear enough. Thanks for your time.
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