Comparing your strace:
[pid 28825] openat(AT_FDCWD, "/dev/ptmx", O_RDWR) = 4
[pid 28825] statfs("/dev/pts", {f_type="TMPFS_MAGIC", f_bsize=4096,
f_blocks=2560, f_bfree=2560,
f_bavail=2560, f_files=2063331, f_ffree=2063053, f_fsid={0, 0}, f_namelen=255,
f_frsize=4096}) = 0
[pid 28825] statfs("/dev/", {f_type="TMPFS_MAGIC", f_bsize=4096, f_blocks=2560,
f_bfree=2560,
f_bavail=2560, f_files=2063331, f_ffree=2063053, f_fsid={0, 0}, f_namelen=255,
f_frsize=4096}) = 0
[pid 28825] close(4) = 0
[pid 28825] openat(AT_FDCWD, "/dev/ptyp0", O_RDWR) = -1 ENOENT (No such file or
directory)
with one on 3.16.0-0.bpo.4-amd64
4023 open("/dev/ptmx", O_RDWR) = 4
4023 statfs("/dev/pts", {f_type="DEVPTS_SUPER_MAGIC", f_bsize=4096, f_blocks=0,
f_bfree=0, f_bavail=0, f_files=0, f_ffree=0, f_fsid={0, 0}, f_namelen=255,
f_frsize=4096}) = 0
4023 ioctl(4, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon echo
...}) = 0
4023 ioctl(4, TIOCGPTN, [2]) = 0
4023 stat("/dev/pts/2", {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 2), ...})
= 0
your trace seems to be "missing" some ioctl() calls on /dev/ptmx.
looking at master.c:
if (!dont_have_tty)
the_pty.pid = forkpty(&the_pty.fd, NULL, &the_pty.term, NULL);
else
the_pty.pid = forkpty(&the_pty.fd, NULL, NULL, NULL);
if (the_pty.pid < 0)
return -1;
i am guessing the difference hides in forkpty. could you
cd /tmp
apt-get source dtach
cd dtach-0.8
./configure
and attach config.h?
stefam
On Fri, Nov 13, 2015 at 04:15:01PM -0400, David Bremner wrote:
> Stefan <b...@bc-bd.org> writes:
>
> > Can you strace detach to see where it looks for ptys ?
>
> Sorry, I missed this message.
>
> Here is the output from strace -f
>
> execve("/usr/bin/dtach", ["dtach", "-A", "/tmp/foo", "bash"], [/* 21 vars
> */]) = 0
> brk(0) = 0x19793000
> faccessat(AT_FDCWD, "/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or
> directory)
> mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
> 0x7f9388e000
> faccessat(AT_FDCWD, "/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or
> directory)
> openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
> fstat(3, {st_mode=S_IFREG|0644, st_size=16627, ...}) = 0
> mmap(NULL, 16627, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f93889000
> close(3) = 0
> faccessat(AT_FDCWD, "/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or
> directory)
> openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libutil.so.1", O_RDONLY|O_CLOEXEC) =
> 3
> read(3,
> "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0\267\0\1\0\0\0\340\17\0\0\0\0\0\0"...,
> 832) = 832
> fstat(3, {st_mode=S_IFREG|0644, st_size=10600, ...}) = 0
> mmap(NULL, 74008, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) =
> 0x7f93854000
> mprotect(0x7f93856000, 61440, PROT_NONE) = 0
> mmap(0x7f93865000, 8192, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1000) = 0x7f93865000
> close(3) = 0
> faccessat(AT_FDCWD, "/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or
> directory)
> openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
> read(3,
> "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0\267\0\1\0\0\0\254\16\2\0\0\0\0\0"...,
> 832) = 832
> fstat(3, {st_mode=S_IFREG|0755, st_size=1275584, ...}) = 0
> mmap(NULL, 1348472, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) =
> 0x7f9370a000
> mprotect(0x7f9383b000, 61440, PROT_NONE) = 0
> mmap(0x7f9384a000, 24576, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x130000) = 0x7f9384a000
> mmap(0x7f93850000, 13176, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f93850000
> close(3) = 0
> mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
> 0x7f93888000
> mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
> 0x7f93887000
> mprotect(0x7f9384a000, 16384, PROT_READ) = 0
> mprotect(0x7f93865000, 4096, PROT_READ) = 0
> mprotect(0x7f93892000, 4096, PROT_READ) = 0
> munmap(0x7f93889000, 16627) = 0
> ioctl(0, TCGETS, {B38400 opost isig icanon echo ...}) = 0
> socket(PF_LOCAL, SOCK_STREAM, 0) = 3
> connect(3, {sa_family=AF_LOCAL, sun_path="/tmp/foo"}, 110) = -1 ENOENT (No
> such file or directory)
> close(3) = 0
> socket(PF_LOCAL, SOCK_STREAM, 0) = 3
> bind(3, {sa_family=AF_LOCAL, sun_path="/tmp/foo"}, 110) = 0
> listen(3, 128) = 0
> fcntl(3, F_GETFL) = 0x2 (flags O_RDWR)
> fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
> fchmodat(AT_FDCWD, "/tmp/foo", 0600) = 0
> fcntl(3, F_SETFD, FD_CLOEXEC) = 0
> pipe2([4, 5], 0) = 0
> fcntl(4, F_SETFD, FD_CLOEXEC) = 0
> fcntl(5, F_SETFD, FD_CLOEXEC) = 0
> clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
> child_tidptr=0x7f938870d0) = 28825
> Process 28825 attached
> [pid 28824] close(5) = 0
> [pid 28825] close(4) = 0
> [pid 28824] read(4, <unfinished ...>
> [pid 28825] setsid() = 28825
> [pid 28825] rt_sigaction(SIGPIPE, {SIG_IGN, [PIPE], SA_RESTART}, {SIG_DFL,
> [], 0}, 8) = 0
> [pid 28825] rt_sigaction(SIGXFSZ, {SIG_IGN, [XFSZ], SA_RESTART}, {SIG_DFL,
> [], 0}, 8) = 0
> [pid 28825] rt_sigaction(SIGHUP, {SIG_IGN, [HUP], SA_RESTART}, {SIG_DFL, [],
> 0}, 8) = 0
> [pid 28825] rt_sigaction(SIGTTIN, {SIG_IGN, [TTIN], SA_RESTART}, {SIG_DFL,
> [], 0}, 8) = 0
> [pid 28825] rt_sigaction(SIGTTOU, {SIG_IGN, [TTOU], SA_RESTART}, {SIG_DFL,
> [], 0}, 8) = 0
> [pid 28825] rt_sigaction(SIGINT, {0x401e74, [INT], SA_RESTART}, {SIG_DFL, [],
> 0}, 8) = 0
> [pid 28825] rt_sigaction(SIGTERM, {0x401e74, [TERM], SA_RESTART}, {SIG_DFL,
> [], 0}, 8) = 0
> [pid 28825] rt_sigaction(SIGCHLD, {0x401e74, [CHLD], SA_RESTART}, {SIG_DFL,
> [], 0}, 8) = 0
> [pid 28825] openat(AT_FDCWD, "/dev/ptmx", O_RDWR) = 4
> [pid 28825] statfs("/dev/pts", {f_type="TMPFS_MAGIC", f_bsize=4096,
> f_blocks=2560, f_bfree=2560, f_bavail=2560, f_files=2063331, f_ffree=2063053,
> f_fsid={0, 0}, f_namelen=255, f_frsize=4096}) = 0
> [pid 28825] statfs("/dev/", {f_type="TMPFS_MAGIC", f_bsize=4096,
> f_blocks=2560, f_bfree=2560, f_bavail=2560, f_files=2063331, f_ffree=2063053,
> f_fsid={0, 0}, f_namelen=255, f_frsize=4096}) = 0
> [pid 28825] close(4) = 0
> [pid 28825] openat(AT_FDCWD, "/dev/ptyp0", O_RDWR) = -1 ENOENT (No such file
> or directory)
> [pid 28825] dup3(5, 1, 0) = 1
> [pid 28825] fstat(1, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
> [pid 28825] mmap(NULL, 65536, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f936fa000
> [pid 28825] unlinkat(AT_FDCWD, "/tmp/foo", 0) = 0
> [pid 28825] write(1, "dtach: init_pty: No such file or"..., 43) = 43
> [pid 28824] <... read resumed> "dtach: init_pty: No such file or"..., 1024) =
> 43
> [pid 28824] write(2, "dtach: init_pty: No such file or"..., 43 <unfinished
> ...>
> [pid 28825] exit_group(1) = ?
> dtach: init_pty: No such file or directory
> [pid 28824] <... write resumed> ) = 43
> [pid 28824] kill(28825, SIGTERM) = 0
> [pid 28824] exit_group(1) = ?
> [pid 28825] +++ exited with 1 +++
> +++ exited with 1 +++
--
One of the most striking differences between a cat and a lie is that a cat has
only nine lives.
-- Mark Twain, "Pudd'nhead Wilson's Calendar"
