[Gllug] Why won't tar access a remote device?

[John Winters]

I have a computer with a couple of tape drives attached to it, which I
use just for backups.  It's off when I'm not doing backups.

It's been working fine for some time but when I came to try to backup
today, the job failed saying that it couldn't access the device.

I use tar on the machine with the files, accessing the tape drive by
means of tar's inbuilt remote device access, piggy-backed onto ssh.  The
thing is - I can't see what it is that tar thinks is failing.  The
following is a (very short) strace of what tar does and I can't see why
it thinks things have gone wrong.  It doesn't even seem to think about
trying to access the remote machine - it just says, "Won't".  Can anyone
see why?

execve("/bin/tar", ["tar", "cvf", "john at duplo:/dev/dat", "bin"], [/* 13
vars */]) = 0
uname({sys="Linux", node="emperor", ...}) = 0
brk(0)                                  = 0x8072000
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0xb7f0f000
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or
directory)
open("/etc/ld.so.preload", O_RDONLY)    = -1 ENOENT (No such file or
directory)
open("/etc/ld.so.cache", O_RDONLY)      = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=56394, ...}) = 0
old_mmap(NULL, 56394, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7f01000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or
directory)
open("/lib/tls/librt.so.1", O_RDONLY)   = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\220\32"...,
512) = 512
fstat64(3, {st_mode=S_IFREG|0644, st_size=22940, ...}) = 0
old_mmap(NULL, 21588, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) =
0xb7efb000
old_mmap(0xb7f00000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED,
3, 0x5000) = 0xb7f00000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or
directory)
open("/lib/tls/libc.so.6", O_RDONLY)    = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0`Z\1\000"...,
512) = 512fstat64(3, {st_mode=S_IFREG|0755, st_size=1254468, ...}) = 0
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0xb7efa000
old_mmap(NULL, 1264780, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) =
0xb7dc5000
old_mmap(0xb7eef000, 36864, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED,
3, 0x129000) = 0xb7eef000
old_mmap(0xb7ef8000, 7308, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|
MAP_ANONYMOUS, -1, 0) = 0xb7ef8000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or
directory)
open("/lib/tls/libpthread.so.0", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0pF\0\000"...,
512) = 512fstat64(3, {st_mode=S_IFREG|0755, st_size=78233, ...}) = 0
old_mmap(NULL, 60772, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) =
0xb7db6000
old_mmap(0xb7dc2000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED,
3, 0xc000) = 0xb7dc2000
old_mmap(0xb7dc3000, 7524, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|
MAP_ANONYMOUS, -1, 0) = 0xb7dc3000
close(3)                                = 0
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0xb7db5000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb7db5080,
limit:1048575, seg_32bit:1, contents:0, read_exec_only:0,
limit_in_pages:1, seg_not_present:0, useable:1}) = 0
munmap(0xb7f01000, 56394)               = 0
set_tid_address(0xb7db50c8)             = 5974
rt_sigaction(SIGRTMIN, {0xb7dba5d0, [], SA_SIGINFO}, NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [RTMIN], NULL, 8) = 0
getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM_INFINITY}) =
0
clock_gettime(CLOCK_REALTIME, {1142173985, 513367000}) = 0
brk(0)                                  = 0x8072000
brk(0x8093000)                          = 0x8093000
brk(0)                                  = 0x8093000
rt_sigaction(SIGCHLD, {SIG_DFL}, {SIG_DFL}, 8) = 0
write(2, "tar: ", 5tar: )                    = 5
write(2, "john at duplo\\:/dev/dat: Cannot ope"..., 33john at duplo\:/dev/dat:
Cannot open) = 33
write(2, ": Input/output error", 20: Input/output error)    = 20
write(2, "\n", 1
)                       = 1
write(2, "tar: ", 5tar: )                    = 5
write(2, "Error is not recoverable: exitin"..., 37Error is not
recoverable: exiting now) = 37
write(2, "\n", 1
)                       = 1
exit_group(2)                           = ?


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