Fact Check: Are not allowed to use this program (crontab)?

Are Users Not Allowed to Use Crontab?

Introduction

The claim in question revolves around the assertion that certain users may not be allowed to use the crontab program, which is a time-based job scheduler in Unix-like operating systems. This claim raises questions about the mechanisms that govern user access to crontab and the specific conditions under which access may be restricted.

What We Know

1. Access Control Mechanisms: The ability to use crontab is primarily controlled through two files: /etc/cron.allow and /etc/cron.deny. If /etc/cron.allow exists, only users listed in this file can use crontab. Conversely, if this file does not exist, all users except those listed in /etc/cron.deny can use crontab. If neither file exists, only the root user has access to crontab 124.

2. Default Behavior: By default, if no restrictions are set (i.e., neither /etc/cron.allow nor /etc/cron.deny exists), all users can create cron jobs. This indicates that the claim about users being unable to use crontab may depend on the specific configuration of these files 24.

3. File Permissions: The permissions of the /etc/cron.allow file are also crucial. For instance, if this file is set to 600, it may prevent non-root users from accessing crontab, effectively denying them the ability to schedule jobs 5.

4. Administrative Control: Even if a user is not listed in cron.allow, they may still be able to run cron jobs as long as they have the necessary permissions and the cron service is configured to allow it. This suggests that the claim may not universally apply to all users, as some may still execute jobs without direct access to crontab 79.

Analysis

The sources consulted provide a mix of factual information and procedural guidelines regarding the use of crontab and its access control mechanisms.

• Source Evaluation:

  • The Geek Search 1 and SUSE Documentation 2 are both technical resources that provide clear explanations of how the cron.allow and cron.deny files function. They are reliable as they come from established platforms that focus on Linux administration.
  • Whitelist 3 and Wafa Tech 4 also offer insights into user restrictions, but they are less formal than the previous two sources and may contain a degree of bias based on their promotional nature.
  • Ask Ubuntu 5 and Stack Overflow 10 provide community-driven insights, which can be useful but may lack the rigor of peer-reviewed or officially sanctioned documentation.

• Methodology and Evidence: The claim's validity hinges on the existence and configuration of the /etc/cron.allow and /etc/cron.deny files. The absence of these files defaults to a permissive state where all users can access crontab. However, the presence of either file can significantly alter this access.

• Conflicts of Interest: Some sources, particularly those that are community-driven or promotional, may have inherent biases. For example, sources that aim to sell security solutions may emphasize the need for restrictions more than necessary, potentially skewing the information presented.

Conclusion

Verdict: Partially True

The assertion that certain users may not be allowed to use crontab is partially true, as access is contingent upon the configuration of the /etc/cron.allow and /etc/cron.deny files. If /etc/cron.allow exists, only users listed there can use crontab. If it does not exist, all users except those in /etc/cron.deny can access it. However, if neither file exists, all users can use crontab, which complicates the claim. Additionally, even users not listed in cron.allow may still execute cron jobs if they have the necessary permissions.

It is important to note that the claim's validity can vary significantly based on specific system configurations and administrative decisions. The evidence does not provide a definitive answer applicable to all scenarios, highlighting the need for context when evaluating user access to crontab.

Readers should be aware that the information presented here is based on the current understanding of crontab access controls, and configurations may differ across systems. Therefore, it is advisable to critically evaluate information and consult system-specific documentation when assessing user permissions.

Sources

1. How cron.allow and cron.deny can be used to limit access to crontab for ... (https://www.thegeeksearch.com/how-cron-allow-and-cron-deny-can-be-user-to-limit-access-to-crontab-for-a-particular-user/)
2. SLES 15 SP6 | Security and Hardening Guide | Restricting cron and at (https://documentation.suse.com/sles/15-SP6/html/SLES-all/cha-sec-cron-at.html)
3. Whitelist: 6 - Linux security: handling usage restrictions for CRON ... (https://www.whitelist1.com/2017/09/6-linux-security-handling-usage.html)
4. Implementing User Restrictions on Cron Job Creation in Linux Servers (https://wafatech.sa/blog/linux/linux-security/implementing-user-restrictions-on-cron-job-creation-in-linux-servers/)
5. 644 Permission needed for /etc/cron.allow, workaround? (https://askubuntu.com/questions/1441454/644-permission-needed-for-etc-cron-allow-workaround)
6. Does cron impose some limitations to types of commands ... (https://unix.stackexchange.com/questions/108177/does-cron-impose-some-limitations-to-types-of-commands-and-privilege-of-executio)
7. 4.1.8 Ensure cron is restricted to authorized users - Tenable (https://www.tenable.com/audits/items/CIS_Ubuntu_Linux_18.04_LTS_v2.2.0_L1_Workstation.audit:08fa37c3e7bd723156db8cf4c449e082)
8. How to restrict cron job execution (https://labex.io/tutorials/cybersecurity-how-to-restrict-cron-job-execution-420297)
9. How to allow or deny users the cron or at command. (https://access.redhat.com/solutions/1535573)
10. How to give permission for the cron job file? - Stack Overflow (https://stackoverflow.com/questions/892104/how-to-give-permission-for-the-cron-job-file)