How to use the command 'getcap' (with examples)

The getcap command is a powerful utility used in UNIX-like systems for retrieving the security capabilities of files. Capabilities are a way to grant specific privileges to files, beyond the traditional user/group/other permissions. This command helps in managing and auditing these capabilities, ensuring files have the correct permissions and reducing the risk of security vulnerabilities.

Use case 1: Get capabilities for the given files

Code:

getcap path/to/file1 path/to/file2 ...

Motivation:

When working with files that require special permissions to execute certain operations, it’s crucial to know what capabilities they possess. This ensures compliance with security policies and helps in troubleshooting permission-related issues. By using the getcap command, system administrators can quickly audit the security capabilities of specific files.

Explanation:

• getcap: This is the command used to fetch the capabilities of files.
• path/to/file1 path/to/file2 ...: Specifies the files whose capabilities you want to retrieve. Replace these placeholders with the actual path(s) of the files you are interested in.

Example output:

/usr/bin/ping = cap_net_admin,cap_net_raw+p
/usr/sbin/hwclock = cap_sys_time+ep

In the output above, /usr/bin/ping has the capabilities cap_net_admin and cap_net_raw, which are necessary for network management, and /usr/sbin/hwclock has cap_sys_time for changing the system’s time.

Use case 2: Get capabilities for all the files recursively under the given directories

Code:

getcap -r path/to/directory1 path/to/directory2 ...

Motivation:

Checking the capabilities of multiple files within directories can be tedious if done individually. The recursive option simplifies this process, making it efficient to audit entire directories. This is particularly useful for system administrators who need to verify the configuration of software installations or system directories for compliance and security.

Explanation:

• getcap: The command to retrieve file capabilities.
• -r: The recursive flag, instructing getcap to check all files under the specified directories and their subdirectories.
• path/to/directory1 path/to/directory2 ...: The directories whose contents you want to analyze. Replace these with the actual paths.

Example output:

/usr/bin/tracepath = cap_net_raw+p
/usr/lib/chromium/chrome-sandbox = cap_sys_admin=ep
/opt/someapp/bin/util = cap_sys_ptrace+ep

In this example, the command traverses the directories and lists capabilities for files like /usr/bin/tracepath, granting raw network operations, and /usr/lib/chromium/chrome-sandbox, with administrative privileges.

Use case 3: Display all searched entries even if no capabilities are set

Code:

getcap -v path/to/file1 path/to/file2 ...

Motivation:

Sometimes, it is not enough to know which files have capabilities set; understanding which files do not have any can also be crucial, especially during detailed audits or security reviews. The verbosity option ensures that you can verify and confirm that the lack of capabilities in certain files is by design and not due to oversight.

Explanation:

• getcap: This is the primary command for retrieving file capabilities.
• -v: The verbose option that forces getcap to display every file specified, even if they have no capabilities set. This is useful for ensuring a comprehensive audit.
• path/to/file1 path/to/file2 ...: These are the files to be checked. Replace them with actual paths of interest.

Example output:

/usr/bin/wget =
/usr/bin/curl = cap_net_bind_service+ep
/usr/bin/scp =

In this example, /usr/bin/wget and /usr/bin/scp have no capabilities set, while /usr/bin/curl has a capability related to network service management.

Conclusion:

Using the getcap command with these specific examples ensures that system administrators and security professionals can effectively audit and manage the capabilities set on files within their systems. By leveraging these options, they can better secure the environment, prevent unauthorized privilege escalation, and maintain strict compliance with security protocols.