I encountered this same bug today. 'plymouth --ping' hangs indeed, this is the strace output: strace plymouth --ping  130 ↵  10015  07:55:41 execve("/bin/plymouth", ["plymouth", "--ping"], [/* 66 vars */]) = 0 brk(NULL) = 0x561d1c4a9000 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) access("/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=105328, ...}) = 0 mmap(NULL, 105328, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f9b0e649000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libply.so.4", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0000E\0\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0644, st_size=88632, ...}) = 0 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f9b0e647000 mmap(NULL, 2185728, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f9b0e226000 mprotect(0x7f9b0e23b000, 2093056, PROT_NONE) = 0 mmap(0x7f9b0e43a000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x14000) = 0x7f9b0e43a000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\340\22\2\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0755, st_size=1960656, ...}) = 0 mmap(NULL, 4061792, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f9b0de46000 mprotect(0x7f9b0e01c000, 2097152, PROT_NONE) = 0 mmap(0x7f9b0e21c000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1d6000) = 0x7f9b0e21c000 mmap(0x7f9b0e222000, 14944, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f9b0e222000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) openat(AT_FDCWD, "/lib/x86_64-linux-gnu/librt.so.1", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\"\0\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0644, st_size=31744, ...}) = 0 mmap(NULL, 2128864, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f9b0dc3e000 mprotect(0x7f9b0dc45000, 2093056, PROT_NONE) = 0 mmap(0x7f9b0de44000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6000) = 0x7f9b0de44000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\220\16\0\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0644, st_size=14632, ...}) = 0 mmap(NULL, 2109712, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f9b0da3a000 mprotect(0x7f9b0da3d000, 2093056, PROT_NONE) = 0 mmap(0x7f9b0dc3c000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7f9b0dc3c000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libpthread.so.0", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\360a\0\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0755, st_size=144776, ...}) = 0 mmap(NULL, 2221160, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f9b0d81b000 mprotect(0x7f9b0d835000, 2093056, PROT_NONE) = 0 mmap(0x7f9b0da34000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x19000) = 0x7f9b0da34000 mmap(0x7f9b0da36000, 13416, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f9b0da36000 close(3) = 0 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f9b0e645000 arch_prctl(ARCH_SET_FS, 0x7f9b0e646040) = 0 mprotect(0x7f9b0e21c000, 16384, PROT_READ) = 0 mprotect(0x7f9b0da34000, 4096, PROT_READ) = 0 mprotect(0x7f9b0dc3c000, 4096, PROT_READ) = 0 mprotect(0x7f9b0de44000, 4096, PROT_READ) = 0 mprotect(0x7f9b0e43a000, 4096, PROT_READ) = 0 mprotect(0x561d1c3c2000, 4096, PROT_READ) = 0 mprotect(0x7f9b0e663000, 4096, PROT_READ) = 0 munmap(0x7f9b0e649000, 105328) = 0 set_tid_address(0x7f9b0e646310) = 13818 set_robust_list(0x7f9b0e646320, 24) = 0 rt_sigaction(SIGRTMIN, {sa_handler=0x7f9b0d820c70, sa_mask=[], sa_flags=SA_RESTORER|SA_SIGINFO, sa_restorer=0x7f9b0d82e150}, NULL, 8) = 0 rt_sigaction(SIGRT_1, {sa_handler=0x7f9b0d820d00, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_SIGINFO, sa_restorer=0x7f9b0d82e150}, NULL, 8) = 0 rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0 prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0 rt_sigaction(SIGPIPE, {sa_handler=SIG_IGN, sa_mask=[PIPE], sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7f9b0de7d140}, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0 brk(NULL) = 0x561d1c4a9000 brk(0x561d1c4ca000) = 0x561d1c4ca000 epoll_create1(EPOLL_CLOEXEC) = 3 pipe2([4, 5], O_CLOEXEC) = 0 epoll_ctl(3, EPOLL_CTL_ADD, 4, {EPOLLERR|EPOLLHUP, {u32=474649408, u64=94683028689728}}) = 0 epoll_ctl(3, EPOLL_CTL_MOD, 4, {EPOLLIN|EPOLLERR|EPOLLHUP, {u32=474649408, u64=94683028689728}}) = 0 openat(AT_FDCWD, "/proc/cmdline", O_RDONLY) = 6 read(6, "BOOT_IMAGE=/boot/vmlinuz-4.13.0-"..., 4096) = 116 close(6) = 0 socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0) = 6 setsockopt(6, SOL_SOCKET, SO_PASSCRED, [1], 4) = 0 connect(6, {sa_family=AF_UNIX, sun_path=@"/org/freedesktop/plymouthd"}, 29) = 0 epoll_ctl(3, EPOLL_CTL_ADD, 6, {EPOLLERR|EPOLLHUP, {u32=474664720, u64=94683028705040}}) = 0 epoll_ctl(3, EPOLL_CTL_MOD, 6, {EPOLLERR|EPOLLHUP, {u32=474664720, u64=94683028705040}}) = 0 epoll_ctl(3, EPOLL_CTL_MOD, 6, {EPOLLOUT|EPOLLERR|EPOLLHUP, {u32=474664720, u64=94683028705040}}) = 0 epoll_pwait(3, [{EPOLLOUT, {u32=474664720, u64=94683028705040}}], 64, -1, NULL, 8) = 1 sendto(6, "P\0", 2, MSG_NOSIGNAL, NULL, 0) = 2 epoll_ctl(3, EPOLL_CTL_MOD, 6, {EPOLLIN|EPOLLOUT|EPOLLERR|EPOLLHUP, {u32=474664720, u64=94683028705040}}) = 0 epoll_ctl(3, EPOLL_CTL_MOD, 6, {EPOLLIN|EPOLLERR|EPOLLHUP, {u32=474664720, u64=94683028705040}}) = 0 epoll_pwait(3, ^Cstrace: Process 13818 detached