Troubleshooting·CompTIA Linux+
Memory, permissions, and what the machine complains about
Domain 5 names memory and permission faults alongside storage, CPU and network. This guide caps a process at 64 MB and watches it swap rather than die, takes the swap away and watches the kernel kill it, then traces a permission denial along every component of a path - and ends with the two commands worth running on any machine you have just been given.
Troubleshooting Guide 13 of 28 Intermediate
- OSUbuntu 26.04 LTS
- Kernel7.0.0-30-generic
- systemd259
- Mandatory access controlAppArmor on Ubuntu, SELinux enforcing on Alma
- TimeAbout 26 min
- Firewallufw / nftables 1.1.6 - firewalld / nftables 1.1.5
| Server Name | IP Address | OS | Roles | CPU | RAM | HDD |
|---|---|---|---|---|---|---|
| LPLUS-A01 | 192.168.0.73 | Ubuntu 26.04 LTS | Debian-family host - apt, ufw, netplan, AppArmor | 2 Core | 4 GB | 50 GB |
This guide includes
Use this when a process is being killed and nothing says why, or when a file with correct permissions cannot be read. This matters because a memory limit without a swap limit does not stop anything, and because the permission that blocks you is usually not on the file you are looking at.
- reading memory, swap and swappiness, and the
/proc/meminfofields that matter - capping a process at 64 MB and finding it swaps rather than dies
- taking swap away and reading the kernel's own OOM record
- tracing a permission denial with
namei -l, which names the component that refused - triaging with
journalctl -p err -bandsystemctl --failed
Before you start
- five-faults-and-the-order-that-finds-them
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What memory the machine has, and what it is doing with it
-
A process given 64 MB, and what it does with the limit
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The same limit, with swap taken away
-
A permission fault, traced along the whole path
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What the machine is complaining about
-
Putting the machine back