我目前能够将手持设备连接到运行 Linux 且运行非常旧的 Ubuntu 14.04 的 PC，将 SynCE 的存储库 PPA 添加到源列表。现在，目标是更新操作系统，我选择了 Debian Buster，我已成功从 Ubuntu Xenial 版本中的同一存储库安装了 DEB 软件包。
在 Debian 中，USB 串行设备被识别并与 ttyUSB 总线连接，获取 IP 地址并在几秒钟后断开连接（两秒，最多三秒）。我已经完成了 PPP 调试（选项 debug dump 和 kdebug），一切看起来都很正常：
pppd options in effect:
debug # (from /etc/ppp/options)
kdebug 7 # (from /etc/ppp/options)
logfile /tmp/pppd.log # (from /etc/ppp/options)
linkname synce-device0 # (from command line)
dump # (from /etc/ppp/options)
noauth # (from command line)
/dev/ttyUSB0 # (from command line)
115200 # (from command line)
lock # (from /etc/ppp/options)
connect /usr/lib/synce-core/synce-serial-chat # (from command line)
record /tmp/pppd.pcap # (from /etc/ppp/options)
crtscts # (from command line)
local # (from command line)
asyncmap 0 # (from /etc/ppp/options)
lcp-echo-failure 4 # (from /etc/ppp/options)
lcp-echo-interval 30 # (from /etc/ppp/options)
hide-password # (from /etc/ppp/options)
ms-dns xxx # [don't know how to print value] # (from command line)
nodefaultroute # (from command line)
192.168.131.1:192.168.131.129 # (from command line)
noipx # (from /etc/ppp/options)
Removed stale lock on ttyUSB0 (pid 4366)
Script /usr/lib/synce-core/synce-serial-chat finished (pid 4435), status = 0x0
Serial connection established.
using channel 14
Using interface ppp0
Connect: ppp0 <--> /dev/pts/3
rcvd [LCP ConfReq id=0x0 <mru 1500> <asyncmap 0x0> <pcomp> <accomp>]
sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0xf230f2eb> <pcomp> <accomp>]
sent [LCP ConfAck id=0x0 <mru 1500> <asyncmap 0x0> <pcomp> <accomp>]
rcvd [LCP ConfAck id=0x1 <asyncmap 0x0> <magic 0xf230f2eb> <pcomp> <accomp>]
sent [LCP EchoReq id=0x0 magic=0xf230f2eb]
sent [CCP ConfReq id=0x1 <deflate 15> <deflate(old#) 15> <bsd v1 15>]
sent [IPCP ConfReq id=0x1 <compress VJ 0f 01> <addr 192.168.131.1>]
rcvd [CCP ConfReq id=0x0 <mppe -H -M -S -L -D +C>]
sent [CCP ConfRej id=0x0 <mppe -H -M -S -L -D +C>]
rcvd [IPCP ConfReq id=0x2 <compress VJ 0f 00> <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-wins 0.0.0.0> <ms-dns2 0.0.0.0> <ms-wins 0.0.0.0>]
sent [IPCP ConfRej id=0x2 <ms-wins 0.0.0.0> <ms-wins 0.0.0.0>]
rcvd [IPV6CP ConfReq id=0x0 <addr fe80::4283:deff:feae:dec9>]
Unsupported protocol 'IPv6 Control Protocol' (0x8057) received
sent [LCP ProtRej id=0x2 80 57 01 00 00 0e 01 0a 42 83 de ff fe ae de c9]
rcvd [LCP EchoRep id=0x0 magic=0x0]
rcvd [CCP ConfRej id=0x1 <deflate 15> <deflate(old#) 15> <bsd v1 15>]
sent [CCP ConfReq id=0x2]
rcvd [IPCP ConfAck id=0x1 <compress VJ 0f 01> <addr 192.168.131.1>]
rcvd [CCP ConfReq id=0x1]
sent [CCP ConfAck id=0x1]
rcvd [IPCP ConfReq id=0x3 <compress VJ 0f 00> <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>]
sent [IPCP ConfNak id=0x3 <addr 192.168.131.129> <ms-dns1 192.168.131.1> <ms-dns2 192.168.131.1>]
rcvd [CCP ConfNak id=0x2 <mppe -H -M -S -L -D +C>]
sent [CCP ConfReq id=0x3]
rcvd [IPCP ConfReq id=0x4 <compress VJ 0f 00> <addr 192.168.131.129> <ms-dns1 192.168.131.1> <ms-dns2 192.168.131.1>]
sent [IPCP ConfAck id=0x4 <compress VJ 0f 00> <addr 192.168.131.129> <ms-dns1 192.168.131.1> <ms-dns2 192.168.131.1>]
local IP address 192.168.131.1
remote IP address 192.168.131.129
Script /etc/ppp/ip-up started (pid 4444)
rcvd [CCP ConfAck id=0x3]
Script /etc/ppp/ip-up finished (pid 4444), status = 0x0
在 UDEV 中，我看到在“添加”事件之后，它从内核触发“删除”，而没有断开设备连接。令人惊讶的是，该事件仅与 ppp0 网络设备相关。
KERNEL[13133.932298] add /devices/pci0000:00/0000:00:06.0/usb2/2-2 (usb)
KERNEL[13133.941859] add /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0 (usb)
KERNEL[13133.946512] add /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0/ttyUSB0 (usb-serial)
KERNEL[13133.946847] add /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0/ttyUSB0/tty/ttyUSB0 (tty)
KERNEL[13133.946887] bind /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0/ttyUSB0 (usb-serial)
KERNEL[13133.946930] bind /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0 (usb)
KERNEL[13133.947016] bind /devices/pci0000:00/0000:00:06.0/usb2/2-2 (usb)
UDEV [13133.951550] add /devices/pci0000:00/0000:00:06.0/usb2/2-2 (usb)
UDEV [13133.967665] add /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0 (usb)
UDEV [13133.969926] add /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0/ttyUSB0 (usb-serial)
UDEV [13133.993251] add /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0/ttyUSB0/tty/ttyUSB0 (tty)
UDEV [13134.002291] bind /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0/ttyUSB0 (usb-serial)
UDEV [13134.003803] bind /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0 (usb)
UDEV [13134.004620] bind /devices/pci0000:00/0000:00:06.0/usb2/2-2 (usb)
KERNEL[13134.445488] add /devices/virtual/net/ppp0 (net)
KERNEL[13134.445509] add /devices/virtual/net/ppp0/queues/rx-0 (queues)
KERNEL[13134.445519] add /devices/virtual/net/ppp0/queues/tx-0 (queues)
UDEV [13134.498959] add /devices/virtual/net/ppp0 (net)
UDEV [13134.510588] add /devices/virtual/net/ppp0/queues/rx-0 (queues)
UDEV [13134.514145] add /devices/virtual/net/ppp0/queues/tx-0 (queues)
<< a little few seconds later >>
KERNEL[13137.624110] remove /devices/virtual/net/ppp0/queues/rx-0 (queues)
KERNEL[13137.624144] remove /devices/virtual/net/ppp0/queues/tx-0 (queues)
KERNEL[13137.624169] remove /devices/virtual/net/ppp0 (net)
UDEV [13137.644633] remove /devices/virtual/net/ppp0/queues/tx-0 (queues)
UDEV [13137.644791] remove /devices/virtual/net/ppp0/queues/rx-0 (queues)
UDEV [13137.659488] remove /devices/virtual/net/ppp0 (net)
该事件与网络接口或网络协议有关，但我还没有看到任何导致它的原因。用Whireshark查看网络流量（记录到pcap文件），我没有发现任何线索。我与 Ubuntu 中的连接进行了比较，但我没有看到任何东西。在 Ubuntu 中，尽管有 RST，连接永远不会丢失（见下图）
https://i.stack.imgur.com/c0RKA.png
在 Debian 上，它突然丢失。
https://i.stack.imgur.com/43vtk.png
目标是在 USB 串行设备和 Linux PC 之间建立 TCP/IP 稳定连接：
ppp0 <--> /dev/ttyUSB0
目前，使用 Debian，连接会在几秒钟（两到三秒钟）内丢失...
Jan 18 20:26:56 debian10 pppd[1590]: local IP address 192.168.131.1
Jan 18 20:26:56 debian10 pppd[1590]: remote IP address 192.168.131.129
Jan 18 20:26:56 debian10 dccm[1505]: DEBUG: synce_device_manager_check_interface_cb: address ready
Jan 18 20:26:56 debian10 dccm[1505]: DEBUG: synce_device_manager_create_device: found device interface for /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0/ttyUSB0/tty/ttyUSB0
Jan 18 20:26:56 debian10 dccm[1505]: DEBUG: synce_device_manager_create_device: listening for device /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0/ttyUSB0/tty/ttyUSB0
Jan 18 20:26:56 debian10 dccm[1505]: DEBUG: synce_device_manager_create_device: NOT triggering connection
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_manager_client_connected_cb: have a connection to port 5679
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_manager_client_connected_cb: creating device object for /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0/ttyUSB0/tty/ttyUSB0
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_set_property: running for device /devices/pci0000:00/0000:00:06.0/usb2/2-2/2-2:1.0/ttyUSB0/tty/ttyUSB0
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_initable_init: connecting to udev
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: info buffer length = 138
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: offset 0: unknown: guint32 ?: 40
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: offset 4: os_major: guint8: 6
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: offset 5: os_minor: guint8: 0
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: offset 6: unknown, build number ?: guint16 ?: 0
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: offset 8: cpu_type: guint16: 2577
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: offset 10: unknown: guint16 ?: 0
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: offset 12: unknown: guint32 ?: 0
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: offset 16: cur_partner_id: guint32: 0
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: offset 20: second partner id ?: guint32 ?: 0
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: offset 24: offset to device name: guint32: 40
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: offset 28: offset to platform name: guint32: 74
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: offset 32: offset to model name: guint32: 104
Jan 18 20:26:57 debian10 dccm[1505]: Message: synce_device_dbus_init: registering object path '/org/synce/dccm/Device/_devices_pci0000_00_0000_00_06_0_usb2_2_2_2_2_1_0_ttyUSB0_tty_ttyUSB0'
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_manager_device_obj_path_changed_cb: sending connected signal for /org/synce/dccm/Device/_devices_pci0000_00_0000_00_06_0_usb2_2_2_2_2_1_0_ttyUSB0_tty_ttyUSB0
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_dbus_init: obj_path set to /org/synce/dccm/Device/_devices_pci0000_00_0000_00_06_0_usb2_2_2_2_2_1_0_ttyUSB0_tty_ttyUSB0
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: get_password_flag_text: setting password flags unset
Jan 18 20:26:57 debian10 dccm[1505]: DEBUG: synce_device_legacy_info_received: setting CTRL_STATE_CONNECTED
Jan 18 20:26:58 debian10 dccm[1505]: DEBUG: gudev_uevent_callback: received uevent **remove** for device /sys/devices/virtual/net/ppp0/queues/tx-0
Jan 18 20:26:58 debian10 dccm[1505]: DEBUG: gudev_uevent_callback: received uevent **remove** for device /sys/devices/virtual/net/ppp0/queues/rx-0
Jan 18 20:26:58 debian10 dccm[1505]: DEBUG: gudev_uevent_callback: received uevent **remove** for device /sys/devices/virtual/net/ppp0
我怎样才能检测到发生了什么？, 内核删除 ppp0 设备的原因是什么？任何有助于解决此问题的答案都将受到高度赞赏，即使有另一种方法可以连接 USB 串行设备，我不知道是否有。
答案1
这udev手册给我答复：
不允许启动守护进程或其他长时间运行的进程；分叉的进程，无论是否分离，都将在事件处理完成后被无条件终止。为了从 udev 规则激活长时间运行的进程，请提供一个服务单元并使用 SYSTEMD_WANTS 设备属性从 udev 设备中将其拉入。
较新的 udev 版本（来自 Ubuntu 16 和 Debian 8）通过对 udev 事务和由它们生成的进程设置严格的时间限制，阻止您在 RUN 或 PROGRAM 脚本中启动长期后台进程。至于对 udev 生成的脚本的长时间运行进程限制，如果您在后台启动某些内容，只要实际的脚本 udev 启动就会很快终止。 Udev 使用 cgroup 来搜索并销毁生成的任务。因此，所有线程都会收到终止信号。
systemd 路线是正确的方法，因为从 udev 启动长时间运行的进程是不允许的。