本文解释为什么show version命令的输出中可能显示系统消息“System returned to ROM by abort”或“System returned to ROM by trace trap”。本文档还解释为什么正在运行的路由器可能返回ROMmon模式。
本文档没有任何特定的要求。
本文档不限于特定的软件和硬件版本。
本文档中的信息都是基于特定实验室环境中的设备编写的。本文档中使用的所有设备最初均采用原始（默认）配置。如果您使用的是真实网络，请确保您已经了解所有命令的潜在影响。
有关文档规则的详细信息，请参阅 Cisco 技术提示规则。
除了硬件和软件版本等信息外，show version命令的输出还显示了有关系统如何重新启动的信息。例如，通过reload命令重新启动的路由器显示消息“System returned to ROM by reload”，而重新启动为重新启动的路由器则显示消息“System returned to ROM by power-on”。 有时，可能会看到以下消息：
Router uptime is 1 minute
System returned to ROM by abort at PC 0x8032A6EC
System image file is "flash:C2600-i-mz.122-10b.bin"
或
Router uptime is 2 minutes
System returned to ROM by trace trap at PC 0x32C2064
System image file is "flash:/c2500-js-l.122-10b"
出现“abort”或“trace trap”消息表示配置寄存器可能已设置为在正常操作中启用中断键的值。位数08(十六进制：0x0 100)（如果已设置），则禁用中断键（即出厂默认值）。 如果重置为0(显式如0x2 0 02中所示，或隐式地(如0x2中所示，等同于0x0 0 02)，则会启用中断键。启用中断键后，中断序列会使路由器进入ROMmon模式，即使路由器已启动并处于正常运行状态。即使没有通过控制台有意发送中断信号，某些行为不当或重新加载的终端也可能意外地向路由器发送类似于中断序列的信号。
有关不同配置寄存器值的详细信息，请参阅配置寄存器位含义。
在 show version 命令的结尾，您可以检查配置寄存器的值：
Router#show version
Cisco Internetwork Operating System Software
IOS (tm) 2500 Software (C2500-JS-L), Version 12.2(10b), RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2002 by cisco Systems, Inc.
Compiled Fri 12-Jul-02 02:13 by pwade
Image text-base: 0x0307AA24, data-base: 0x00001000
ROM: System Bootstrap, Version 11.0(10c), SOFTWARE
BOOTLDR: 3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c), RELEASE SOFTWARE (fc1)
R1 uptime is 9 minutes
System returned to ROM by trace trap at PC 0x32C2064
System image file is "flash:/c2500-js-l.122-10b"
cisco 2500 (68030) processor (revision F) with 16384K/2048K bytes of memory.
Processor board ID 04796554, with hardware revision 00000000
Bridging software.
X.25 software, Version 3.0.0.
SuperLAT software (copyright 1990 by Meridian Technology Corp).
TN3270 Emulation software.
Basic Rate ISDN software, Version 1.1.
1 Ethernet/IEEE 802.3 interface(s)
2 Serial network interface(s)
1 ISDN Basic Rate interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read ONLY)
Configuration register is 0x2002
为防止路由器无意中返回ROMmon模式，请将配置寄存器更改为禁用中断键的值。为此，请将配置寄存器的第8位更改为1（最常用值为0x2102）。
Router>enable
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#config-register 0x2102
Router(config)#^Z
00:20:13: %SYS-5-CONFIG_I: Configured from console by console
Router#show version
Cisco Internetwork Operating System Software
IOS (tm) 2500 Software (C2500-JS-L), Version 12.2(10b), RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2002 by cisco Systems, Inc.
Compiled Fri 12-Jul-02 02:13 by pwade
Image text-base: 0x0307AA24, data-base: 0x00001000
ROM: System Bootstrap, Version 11.0(10c), SOFTWARE
BOOTLDR: 3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c), RELEASE SOFTWARE (fc1)
Router uptime is 20 minutes
System returned to ROM by trace trap at PC 0x32C2064
System image file is "flash:/c2500-js-l.122-10b"
cisco 2500 (68030) processor (revision F) with 16384K/2048K bytes of memory.
Processor board ID 04796554, with hardware revision 00000000
Bridging software.
X.25 software, Version 3.0.0.
SuperLAT software (copyright 1990 by Meridian Technology Corp).
TN3270 Emulation software.
Basic Rate ISDN software, Version 1.1.
1 Ethernet/IEEE 802.3 interface(s)
2 Serial network interface(s)
1 ISDN Basic Rate interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read ONLY)
Configuration register is 0x2002 (will be 0x2102 at next reload)
配置寄存器的第8位设置后，系统将受到保护，以免出现中断信号，否则这些信号可能会导致路由器进入ROMmon模式。新的配置寄存器设置仅在下次重新加载时生效。确保在禁用中断键之前为此路由器安排停机时间。
注意：在路由器重新加载或通电后（在启动序列期间），无论配置寄存器中第八位的状态如何，在前60秒内始终启用中断密钥。如果通过配置寄存器禁用或启用中断密钥，则路由器仅在正常操作期间受影响，在启动序列期间不受影响。
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