How Can I Locate Faults Using an Exit Code?

When a container fails to be started or terminated, the exit code is recorded by Kubernetes events to report the cause. This section describes how to locate faults using an exit code.

Viewing an Exit Code

You can use kubectl to connect to the cluster and run the following command to check the pod:

kubectl describe pod {pod name}

In the command output, the Exit Code field indicates the status code of the last program exit. If the value is not 0, the program exits abnormally. You can further analyze the cause through this code.

Containers: 
  container-1: 
    Container ID: ... 
    Image: ... 
    Image ID: ... 
    Ports: ... 
    Host Ports: ... 
    Args: ... 
    State: Running    
      Started: Sat, 28 Jan 2023 09:06:53 +0000 
    Last State: Terminated    
      Reason: Error    
      Exit Code: 255    
      Started: Sat, 28 Jan 2023 09:01:33 +0000    
      Finished: Sat, 28 Jan 2023 09:05:11 +0000 
    Ready: True 
    Restart Count: 1

Description

The exit code ranges from 0 to 255.

If the exit code is 0, the container exits normally.
Generally, if the abnormal exit is caused by the program, the exit code ranges from 1 to 128. In special scenarios, the exit code ranges from 129 to 255.
When a program exits due to external interrupts, the exit code ranges from 129 to 255. When the operating system sends an interrupt signal to the program, the exist code is the interrupt signal value plus 128. For example, if the interrupt signal value of SIGKILL is 9, the exit status code is 137 (9 + 128).
If the exist code is not in the range of 0 to 255, for example, exit(-1), the exit code is automatically converted to a value that is within this range.
If the exist code is a positive number, the conversion formula is as follows:
```
code % 256
```
If the exit code is a negative number, the conversion formula is as follows:
```
256 - (|code| % 256)
```

For details, see Exit Codes With Special Meanings.

Common Exit Codes

**Table 1** Common exit codes
Exit Code	Name	Description
0	Normal exit	The container exits normally. This status code does not always indicate that an exception occurs. When there is no process in the container, it may also be displayed.
1	Common program error	There are many causes for this exception, most of which are caused by the program. You need to further locate the cause through container logs. For example, this error occurs when an x86 image is running on an Arm node.
125	The container is not running.	The possible causes are as follows: An undefined flag is used in the command, for example, docker run --abcd. The user-defined command in the image has insufficient permissions on the local host. The container engine is incompatible with the host OS or hardware.
126	Command calling error	The command called in the image cannot be executed. For example, the file permission is insufficient or the file cannot be executed.
127	The file or directory cannot be found.	The file or directory specified in the image cannot be found.
128	Invalid exit parameter	The container exits but no valid exit code is provided. There are multiple possible causes. You need to further locate the cause. For example, an application running on the containerd node attempts to call the docker command.
137	Immediate termination (SIGKILL)	The program is terminated by the SIGKILL signal. The common causes are as follows: The memory usage of the container in the pod reaches the resource limit. For example, OOM causes cgroup to forcibly stop the container. If OOM occurs, the kernel of the node stops some processes to release the memory. As a result, the container may be terminated. If the container health check fails, kubelet stops the container. Other external processes, such as malicious scripts, forcibly stop the container.
139	Segmentation error (SIGSEGV)	The container receives the SIGSEGV signal from the OS because the container attempts to access an unauthorized memory location.
143	Graceful termination (SIGTERM)	The container is correctly closed as instructed by the host. Generally, this exit code 143 does not require troubleshooting.
255	The exit code is out of range.	The container exit code is out of range. For example, exit(-1) may be used for abnormal exit, and -1 is automatically converted to 255. Further troubleshooting is required.

Linux Standard Interrupt Signals

You can run the kill -l command to view the signals and corresponding values in the Linux OS.

**Table 2** Common Linux standard interrupt signals
Signal	Value	Action	Commit
SIGHUP	1	Term	Sent when the user terminal connection (normal or abnormal) ends.
SIGINT	2	Term	Program termination signal, which is sent by the terminal by pressing Ctrl+C.
SIGQUIT	3	Core	Similar to SIGINT, the exit command is sent by the terminal. Generally, the exit command is controlled by pressing Ctrl+\.
SIGILL	4	Core	Invalid instruction, usually because an error occurs in the executable file.
SIGABRT	6	Core	Signal generated when the abort function is invoked. The process ends abnormally.
SIGFPE	8	Core	A floating-point arithmetic error occurs. Other arithmetic errors such as divisor 0 also occur.
SIGKILL	9	Term	Any process is terminated.
SIGSEGV	11	Core	Attempt to access an unauthorized memory location.
SIGPIPE	13	Term	The pipe is disconnected.
SIGALRM	14	Term	Indicates clock timing.
SIGTERM	15	Term	Process end signal, which is usually the normal exit of the program.
SIGUSR1	10	Term	This is a user-defined signal in applications.
SIGUSR2	12	Term	This is a user-defined signal in applications.
SIGCHLD	17	Ign	This signal is generated when a subprocess ends or is interrupted.
SIGCONT	18	Cont	Resume a stopped process.
SIGSTOP	19	Stop	Suspend the execution of a process.
SIGTSTP	20	Stop	Stop a process.
SIGTTIN	21	Stop	The background process reads the input value from the terminal.
SIGTTOU	22	Stop	The background process reads the output value from the terminal.