> ## Documentation Index > Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt > Use this file to discover all available pages before exploring further. # Exit Codes > This article explores exit codes in shell scripts, indicating command success or failure on Linux systems. In this article, we explore the concept of exit codes in shell scripts and how they indicate whether a command executed successfully or encountered an error on Linux systems. When you run a command, it either executes successfully or fails. For instance, listing the contents of the current directory with the command below executes successfully and returns an exit status of zero: ```bash theme={null} $ ls /home/root/tmp ``` Conversely, if you run a command that does not exist, an error is displayed and a non-zero exit code is returned: ```bash theme={null} $ lss Failed: command not found ``` When a command runs successfully, it returns an exit status of 0; when it fails, it returns a non-zero value. These exit codes are not shown in the command output but are stored in the built-in variable "\$?". To view the exit code immediately after executing a command, use: ```bash theme={null} $ ls /home/root/tmp $ echo $? 0 $ lss Failed: command not found $ echo $? 127 ``` It is considered best practice to use exit codes in your scripts to communicate the overall status to the caller or user. Consider a scenario where you are launching a rocket mission. For a successful launch, the script should return an exit status of 0, and for any failure, it should explicitly return a non-zero value (commonly 1). Below is a sample script that starts a rocket launch mission. In this naive version, even if the launch fails, the script returns an exit code of 0 because it only prints a failure message without setting a non-zero index: ```bash theme={null} mkdir $mission_name rocket-add $mission_name rocket-start-power $mission_name rocket-internal-power $mission_name rocket-start-sequence $mission_name rocket-start-engine $mission_name rocket-lift-off $mission_name rocket_status=$(rocket-status $mission_name) while [ "$rocket_status" == "launching" ] do sleep 2 rocket_status=$(rocket-status $mission_name) done if [ "$rocket_status" = "failed" ] then rocket-debug $mission_name fi ``` If you run the script, the output might be: ```bash theme={null} $ create-and-launch-rocket failed ``` However, checking the exit code reveals that it remains 0: ```bash theme={null} $ echo $? 0 ``` To address this issue, update the script so that it returns a non-zero exit code (typically 1) when the launch fails. Here is the improved version of the script: ```bash theme={null} mkdir $mission_name rocket-add $mission_name rocket-start-power $mission_name rocket-internal-power $mission_name rocket-start-sequence $mission_name rocket-start-engine $mission_name rocket-lift-off $mission_name rocket_status=$(rocket-status $mission_name) while [ "$rocket_status" == "launching" ] do sleep 2 rocket_status=$(rocket-status $mission_name) done if [ "$rocket_status" = "failed" ] then rocket-debug $mission_name exit 1 fi ``` Now, if the rocket launch fails, the script will correctly exit with a status code of 1. This can be verified as follows: ```bash theme={null} $ create-and-launch-rocket failed ``` ```bash theme={null} $ echo $? 1 ``` Always ensure that your scripts return an appropriate exit code. Explicitly returning a non-zero code for failure conditions facilitates better integration with other systems and scripts.