Senior DevOps / SRE [L2] Linux Linux / SRE — Scenario-Based Interview Questions Production Scenario [L2]

Q: An ex-employee changed the root password of a critical bare-metal Linux server and left. You have physical access to the server but do not know the password. How do you regain control?

\"In an interview, I explain my systematic Linux troubleshooting methodology using Brendan Gregg's USE method. The interviewer is testing: GRUB manipulation, Rescue Mode, `rd.break`.. I structure my answer around systematic triage first, root cause analysis second, and permanent remediation third.\" Key Strategy: Pro-Tip: Reboot the server. When the GRUB menu appears, press e to edit the kernel boot parameters..

Since physical access is available, the root password can be reset by interrupting the bootloader (GRUB).

#Linux #Linux / SRE — Scenario-Based Interview Questions #L2 #SRE #Systems #Troubleshooting

🎙️ Candidate Opening & Architectural Context

""In an interview, I explain my systematic Linux troubleshooting methodology using Brendan Gregg's USE method. The interviewer is testing: GRUB manipulation, Rescue Mode, `rd.break`.. I structure my answer around systematic triage first, root cause analysis second, and permanent remediation third.""

🛠️ Production Runbook & Step-by-Step Resolution

1️⃣

Initial Diagnostics & Root Cause Analysis

Since physical access is available, the root password can be reset by interrupting the bootloader (GRUB).

Reboot the server. When the GRUB menu appears, press e to edit the kernel boot parameters.
Find the line starting with linux or linux16. Append rd.break (on RHEL/CentOS) or init=/bin/bash (on Debian/Ubuntu) to the end of that line, and press Ctrl+X to boot.
This drops you into an emergency root shell *before* the system fully mounts or asks for a password.

2️⃣

Remediation & Permanent Safeguards

Mount the actual root filesystem mathematically with read-write access: mount -o remount,rw /sysroot and chroot /sysroot.
Run the passwd command to comfortably set a new root password. Exit and reboot.

💡 The Senior SRE Gold Nugget (Key Architectural Takeaway)

"Pro-Tip: Reboot the server. When the GRUB menu appears, press e to edit the kernel boot parameters.."

⚡ 60-Second Elevator Pitch Talking Points

Reboot the server. When the GRUB menu appears, press e to edit the kernel boot parameters.
Find the line starting with linux or linux16. Append rd.break (on RHEL/CentOS) or init=/bin/bash ...
This drops you into an emergency root shell *before* the system fully mounts or asks for a password.

Q: An ex-employee changed the root password of a critical bare-metal Linux server and left. You have physical access to the server but do not know the password. How do you regain control?

🛠️ Production Runbook & Step-by-Step Resolution

Initial Diagnostics & Root Cause Analysis

Remediation & Permanent Safeguards

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