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Monitoring and Troubleshooting

This chapter introduces the basics for monitoring and troubleshooting Cumulus Linux.

Serial Console

The serial console is a useful tool for debugging issues, especially when you find yourself rebooting the switch often or if you do not have a reliable network connection.

The default serial console baud rate is 115200, which is the baud rate ONIE uses.

Configure the Serial Console on ARM Switches

On ARM switches, the U-Boot environment variable baudrate identifies the baud rate of the serial console. To change the baudrate variable, use the fw_setenv command:

cumulus@switch:~$ sudo fw_setenv baudrate 9600
Updating environment variable: `baudrate'
Proceed with update [N/y]? y

You must reboot the switch for the baudrate change to take effect.

The valid values for baudrate are:

  • 300
  • 600
  • 1200
  • 2400
  • 4800
  • 9600
  • 19200
  • 38400
  • 115200

Configure the Serial Console on x86 Switches

On x86 switches, you configure serial console baud rate by editing grub.

Incorrect configuration settings in grub can cause the switch to be inaccessible via the console. Review grub changes carefully before you implement them.

The valid values for the baud rate are:

  • 300
  • 600
  • 1200
  • 2400
  • 4800
  • 9600
  • 19200
  • 38400
  • 115200

To change the serial console baud rate:

  1. Edit the /etc/default/grub file. The two relevant lines in /etc/default/grub are as follows; replace the 115200 value with a valid value specified above in the --speed variable in the first line and in the console variable in the second line:

    GRUB_SERIAL_COMMAND="serial --port=0x2f8 --speed=115200 --word=8 --parity=no --stop=1"
    GRUB_CMDLINE_LINUX="console=ttyS1,115200n8 cl_platform=accton_as5712_54x"
  2. After you save your changes to the grub configuration, type the following at the command prompt:

    cumulus@switch:~$ update-grub
  3. If you plan on accessing the switch BIOS over the serial console, you need to update the baud rate in the switch BIOS. For more information, see this knowledge base article.

  4. Reboot the switch.

Change the Console Log Level

By default, the console prints all log messages except debug messages. To tune console logging to be less verbose so that certain levels of messages are not printed, run the dmesg -n <level> command, where the log levels are:

0Emergency messages (the system is about to crash or is unstable).
1Serious conditions; you must take action immediately.
2Critical conditions (serious hardware or software failures).
3Error conditions (often used by drivers to indicate difficulties with the hardware).
4Warning messages (nothing serious but might indicate problems).
5Message notifications for many conditions, including security events.
6Informational messages.
7Debug messages.

Only messages with a value lower than the level specified are printed to the console. For example, if you specify level 3, only level 2 (critical conditions), level 1 (serious conditions), and level 0 (emergency messages) are printed to the console:

cumulus@switch:~$ sudo dmesg -n 3

Alternatively, you can run dmesg --console-level <level> command, where the log levels are emerg, alert, crit, err, warn, notice, info, or debug. For example, to print critical conditions, run the following command:

cumulus@switch:~$ sudo dmesg --console-level crit

The dmesg command is applied until the next reboot.

For more details about the dmesg command, run man dmesg.

Show General System Information

Two commands are helpful for getting general information about the switch and the version of Cumulus Linux you are running. These are helpful with system diagnostics and if you need to submit a support request.

For information about the version of Cumulus Linux running on the switch, run the net show version,command which displays the contents of /etc/lsb-release:

cumulus@switch:~$ net show version
DISTRIB_ID="Cumulus Linux"
DISTRIB_DESCRIPTION="Cumulus Linux 4.1.0"

For general information about the switch, run net show system, which gathers information about the switch from a number of files in the system:

cumulus@switch:~$ net show system
Hostname......... celRED

Build............ Cumulus Linux 4.1.0
Uptime........... 8 days, 12:24:01.770000

Model............ Cel REDSTONE
CPU.............. x86_64 Intel Atom C2538 2.4 GHz
Memory........... 4GB
Disk............. 14.9GB
ASIC............. Broadcom Trident2 BCM56854
Ports............ 48 x 10G-SFP+ & 6 x 40G-QSFP+
Base MAC Address. a0:00:00:00:00:50

Diagnostics Using cl-support

You can use cl-support to generate a single export file that contains various details and the configuration from a switch. This is useful for remote debugging and troubleshooting. For more information about cl-support, read Understanding the cl-support Output File.

Run cl-support before you submit a support request as this file helps in the investigation of issues.

cumulus@switch:~$ sudo cl-support -h
Usage: [-h (help)] [-cDjlMsv] [-d m1,m2,...] [-e m1,m2,...]
  [-p prefix] [-r reason] [-S dir] [-T Timeout_seconds] [-t tag]
  -h: Display this help message
  -c: Run only modules matching any core files, if no -e modules
  -D: Display debugging information
  -d: Disable (do not run) modules in this comma separated list
  -e: Enable (only run) modules in this comma separated list; "-e all" runs
      all modules and sub-modules, including all optional modules

Send Log Files to a syslog Server

You can configure the remote syslog server on the switch using the following configuration:

cumulus@switch:~$ net add syslog host ipv4 port udp 514
cumulus@switch:~$ net pending
cumulus@switch:~$ net commit

This creates a file called /etc/rsyslog.d/11-remotesyslog.conf in the rsyslog directory. The file has the following content:

cumulus@switch:~$ cat /etc/rsyslog.d/11-remotesyslog.conf
# This file was automatically generated by NCLU.
*.*   @   # UDP

NCLU cannot configure a remote syslog if management VRF is enabled on the switch. Refer to Monitoring and Troubleshooting below.

Log Technical Details

Logging on Cumulus Linux is done with rsyslog. rsyslog provides both local logging to the syslog file as well as the ability to export logs to an external syslog server. High precision timestamps are enabled for all rsyslog log files; for example:

2015-08-14T18:21:43.337804+00:00 cumulus switchd[3629]: switchd.c:1409 switchd version 1.0-cl2.5+5

There are applications in Cumulus Linux that can write directly to a log file without going through rsyslog. These files are typically located in /var/log/.

All Cumulus Linux rules are stored in separate files in /etc/rsyslog.d/, which are called at the end of the GLOBAL DIRECTIVES section of /etc/rsyslog.conf. As a result, the RULES section at the end of rsyslog.conf is ignored because the messages have to be processed by the rules in /etc/rsyslog.d and then dropped by the last line in /etc/rsyslog.d/99-syslog.conf.

Local Logging

Most logs within Cumulus Linux are sent through rsyslog, which writes them to files in the /var log directory. There are default rules in the /etc/rsyslog.d/ directory that define where the logs are written:

10-rules.confSets defaults for log messages, include log format and log rate limits.
15-crit.confLogs crit, alert or emerg log messages to /var/log/crit.log to ensure they are not rotated away rapidly.
20-clagd.confLogs clagd messages to /var/log/clagd.log for MLAG.
22-linkstate.confLogs link state changes for all physical and logical network links to /var/log/linkstate.
25-switchd.confLogs switchd messages to /var/log/switchd.log.
30-ptmd.confLogs ptmd messages to /var/log/ptmd.log for Prescription Topology Manager.
35-rdnbrd.confLogs rdnbrd messages to /var/log/rdnbrd.log for Redistribute Neighbor.
40-netd.confLogs netd messages to /var/log/netd.log for NCLU.
45-frr.confLogs routing protocol messages to /var/log/frr/frr.log. This includes BGP and OSPF log messages.
99-syslog.confAll remaining processes that use rsyslog are sent to /var/log/syslog.

Log files that are rotated are compressed into an archive. Processes that do not use rsyslog write to their own log files within the /var/log directory. For more information on specific log files, see Troubleshooting Log Files.

Enable Remote syslog

By default, not all log messages are sent to a remote server. To send other log files (such as switchd logs) to a syslog server, follow these steps:

  1. Create a file in /etc/rsyslog.d/. Make sure the filename starts with a number lower than 99 so that it executes before log messages are dropped in, such as 20-clagd.conf or 25-switchd.conf. The example file below is called /etc/rsyslog.d/11-remotesyslog.conf. Add content similar to the following:

    ## Logging switchd messages to remote syslog server

    This configuration sends log messages to a remote syslog server for the following processes: clagd, switchd, ptmd, rdnbrd, netd and syslog. It follows the same syntax as the /var/log/syslog file, where @ indicates UDP, 192.168.12 is the IP address of the syslog server, and 514 is the UDP port.

    • For TCP-based syslog, use two @@ before the IP address @@
    • The numbering of the files in /etc/rsyslog.d/ dictates how the rules are installed into rsyslog.d. Lower numbered rules are processed first, and rsyslog processing terminates with the stop keyword. For example, the rsyslog configuration for FRR is stored in the 45-frr.conf file with an explicit stop at the bottom of the file. FRR messages are logged to the /var/log/frr/frr.log file on the local disk only (these messages are not sent to a remote server using the default configuration). To log FRR messages remotely in addition to writing FRR messages to the local disk, rename the 99-syslog.conf file to 11-remotesyslog.conf. FRR messages are first processed by the 11-remotesyslog.conf rule (transmit to remote server), then continue to be processed by the 45-frr.conf file (write to local disk in the /var/log/frr/frr.log file).
    • Do not use the imfile module with any file written by rsyslogd.

  2. Restart rsyslog.

    cumulus@switch:~$ sudo systemctl restart rsyslog.service

Write to syslog with Management VRF Enabled

You can write to syslog with management VRF enabled by applying the following configuration; this configuration is commented out in the /etc/rsyslog.d/11-remotesyslog.conf file:

cumulus@switch:~$ cat /etc/rsyslog.d/11-remotesyslog.conf
## Copy all messages to the remote syslog server at port 514
action(type="omfwd" Target="" Device="mgmt" Port="514" Protocol="udp")

For each syslog server, configure a unique action line. For example, to configure two syslog servers at and

cumulus@switch:~$ cat /etc/rsyslog.d/11-remotesyslog.conf
## Copy all messages to the remote syslog servers at and port 514
action(type="omfwd" Target="" Device="mgmt" Port="514" Protocol="udp")
action(type="omfwd" Target="" Device="mgmt" Port="514" Protocol="udp")

If you configure remote logging to use the TCP protocol, local logging might stop when the remote syslog server is unreachable. To avoid this behavior, configure a disk queue size and maximum retry count in your rsyslog configuration:

action(type="omfwd" Target="" Device="mgmt" Port="1720" Protocol="tcp" action.resumeRetryCount="100" queue.type="linkedList" queue.size="10000")

Rate-limit syslog Messages

If you want to limit the number of syslog messages that can be written to the syslog file from individual processes, add the following configuration to the /etc/rsyslog.conf file. Adjust the interval and burst values to rate-limit messages to the appropriate levels required by your environment. For more information, read the rsyslog documentation.

      SysSock.RateLimit.Interval="2" SysSock.RateLimit.Burst="50")

The following test script shows an example of rate-limit outputvin Cumulus Linux

Example test script

Harmless syslog Error: Failed to reset devices.list

The following message is logged to /var/log/syslog when you run systemctl daemon-reload and during system boot:

systemd[1]: Failed to reset devices.list on /system.slice: Invalid argument

This message is harmless, and can be ignored. It is logged when systemd attempts to change group attributes that are read only. The upstream version of systemd has been modified to not log this message by default.

The systemctl daemon-reload command is often issued when Debian packages are installed, so the message may be seen multiple times when upgrading packages.

Syslog Troubleshooting Tips

You can use the following commands to troubleshoot syslog issues.

Verifying that rsyslog is Running

To verify that the rsyslog service is running, use the sudo systemctl status rsyslog.service command:

cumulus@leaf01:mgmt-vrf:~$ sudo systemctl status rsyslog.service
rsyslog.service - System Logging Service
  Loaded: loaded (/lib/systemd/system/rsyslog.service; enabled)
  Active: active (running) since Sat 2017-12-09 00:48:58 UTC; 7min ago
    Docs: man:rsyslogd(8)
Main PID: 11751 (rsyslogd)
  CGroup: /system.slice/rsyslog.service
          └─11751 /usr/sbin/rsyslogd -n

Dec 09 00:48:58 leaf01 systemd[1]: Started System Logging Service.

Verify your rsyslog Configuration

After making manual changes to any files in the /etc/rsyslog.d directory, use the sudo rsyslogd -N1 command to identify any errors in the configuration files that might prevent the rsyslog service from starting.

In the following example, a closing parenthesis is missing in the 11-remotesyslog.conf file, which is used to configure syslog for management VRF:

cumulus@leaf01:mgmt-vrf:~$ cat /etc/rsyslog.d/11-remotesyslog.conf
action(type="omfwd" Target="" Device="mgmt" Port="514" Protocol="udp"

cumulus@leaf01:mgmt-vrf:~$ sudo rsyslogd -N1
rsyslogd: version 8.4.2, config validation run (level 1), master config /etc/rsyslog.conf
syslogd: error during parsing file /etc/rsyslog.d/15-crit.conf, on or before line 3: invalid character '$' in object definition - is there an invalid escape sequence somewhere? [try http: /www.rsyslog.com/e/2207 ]
rsyslogd: error during parsing file /etc/rsyslog.d/15-crit.conf, on or before line 3: syntax error on token 'crit_log' [try http://www.rsyslog.com/e/2207 ]

After correcting the invalid syntax, issuing the sudo rsyslogd -N1 command produces the following output.

cumulus@leaf01:mgmt-vrf:~$ cat /etc/rsyslog.d/11-remotesyslog.conf
action(type="omfwd" Target="" Device="mgmt" Port="514" Protocol="udp")
cumulus@leaf01:mgmt-vrf:~$ sudo rsyslogd -N1
rsyslogd: version 8.4.2, config validation run (level 1), master config /etc/rsyslog.conf
rsyslogd: End of config validation run. Bye.


If a syslog server is not accessible to validate that syslog messages are being exported, you can use tcpdump.

In the following example, a syslog server has been configured at for UDP syslogs on port 514:

cumulus@leaf01:mgmt-vrf:~$ sudo tcpdump -i eth0 host and udp port 514

A simple way to generate syslog messages is to use sudo in another session, such as sudo date. Using sudo generates an authpriv log.

cumulus@leaf01:mgmt-vrf:~$ sudo tcpdump -i eth0 host and udp port 514
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
00:57:15.356836 IP leaf01.lab.local.33875 > SYSLOG authpriv.notice, length: 105
00:57:15.364346 IP leaf01.lab.local.33875 > SYSLOG authpriv.info, length: 103
00:57:15.369476 IP leaf01.lab.local.33875 > SYSLOG authpriv.info, length: 85

To see the contents of the syslog file, use the tcpdump -X option:

cumulus@leaf01:mgmt-vrf:~$ sudo tcpdump -i eth0 host and udp port 514 -X -c 3
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
00:59:15.980048 IP leaf01.lab.local.33875 > SYSLOG authpriv.notice, length: 105
0x0000: 4500 0085 33ee 4000 4011 8420 c0a8 000b E...3.@.@.......
0x0010: c0a8 00fe 8453 0202 0071 9d18 3c38 353e .....S...q..<85>
0x0020: 4465 6320 2039 2030 303a 3539 3a31 3520 Dec..9.00:59:15.
0x0030: 6c65 6166 3031 2073 7564 6f3a 2020 6375 leaf01.sudo:..cu
0x0040: 6d75 6c75 7320 3a20 5454 593d 7074 732f mulus.:.TTY=pts/
0x0050: 3120 3b20 5057 443d 2f68 6f6d 652f 6375 1.;.PWD=/home/cu
0x0060: 6d75 6c75 7320 3b20 5553 4552 3d72 6f6f mulus.;.USER=roo
0x0070: 7420 3b20 434f 4d4d 414e 443d 2f62 696e t.;.COMMAND=/bin
0x0080: 2f64 6174 65 /date