linux-disk-storage

Disk & Storage

Distro support

Core tools (df, du, lsblk, ncdu, findmnt, fdisk) are identical on both families. The differences are package-cache cleanup, sandboxed-package storage, and the default root filesystem. Body uses Debian/Ubuntu; the RHEL family (Fedora, RHEL, CentOS Stream, Rocky, Alma, Oracle) equivalents are in the matrix.

Concept	Debian/Ubuntu	RHEL family
Package cache cleanup	`apt clean` / `apt autoclean`	`dnf clean all`
Remove orphan pkgs	`apt autoremove`	`dnf autoremove`
Journal disk usage	`journalctl --disk-usage` / `--vacuum-size`	same
Sandboxed apps storage	`/var/lib/snapd`, `snap` revisions	`flatpak` / none on servers
Default root FS	usually `ext4`	usually `xfs`
df / du / lsblk / ncdu	identical	identical
CIFS/SMB client + `mount.cifs`	`apt install cifs-utils`	`dnf install cifs-utils`
SMB share discovery (`smbclient -L`)	`apt install smbclient`	`dnf install samba-client`
`mount -t cifs` / NFS / fstab / autofs	identical	identical

RHEL-family gotcha: the default root filesystem is usually XFS, which cannot be shrunk (only grown with xfs_growfs). On Debian/Ubuntu it is usually ext4 (shrinkable). Plan partition resizes accordingly. LVM operations are identical on both.

In sk-* scripts use the common.sh package primitives (pkg_update, etc.) rather than hardcoding apt/dnf. See linux-bash-scripting and docs/multi-distro/plan.md.

Use when

Investigating disk pressure, inode exhaustion, or storage-related outages.
Cleaning up safe space hogs on a server.
Adding swap on a host that is currently running without one.
Mounting a network share (NFS, or a Windows/NAS SMB share via CIFS) on a Linux client.

Do not use when

The issue is mainly application slowness or CPU pressure; use linux-system-monitoring or linux-troubleshooting.
The task is filesystem permissions or user access; use linux-access-control.
The task is point-in-time snapshots — LVM snapshots, or ZFS/Btrfs (zfs snapshot/zfs send, btrfs subvolume snapshot/btrfs send). That now lives in 13-backup-and-archiving/linux-filesystem-snapshots. This skill keeps LVM volume management, fstab, NFS, and CIFS/SMB.

Required Inputs

Artefact	Source	Required?	If absent
Target host and filesystem/path	Operator, alert, or `findmnt` output	yes	Inspect read-only; do not assume the affected mount
Intended outcome	Incident owner: diagnose, cleanup, resize, swap, NFS, or CIFS	yes	Return diagnosis and options only
Retention and deletion authority	Service owner or retention policy	for deletion	Do not delete logs, backups, caches, or application data
Credentials and ownership mapping	Approved secret provider and application owner	for CIFS	Do not create a CIFS mount

Capability Contract

Read/search diagnosis needs shell access to df, du, findmnt, and lsblk. Cleanup, partition, swap, mount, and /etc/fstab changes require explicit root-level change authority. Never reveal share credentials or infer deletion approval from disk pressure.

Degraded Mode

If root, package tools, network reachability, credentials, or a maintenance window is unavailable, report the observable usage and the exact unassessed operation. Provide safe commands for an operator; do not mark capacity, mount persistence, or boot safety as passed.

Decision Rules

Condition	Action	Failure avoided
Inodes exhausted but blocks remain	Locate high-file-count directories	Deleting large files that cannot fix inode pressure
Filesystem is XFS	Grow or migrate; never plan an in-place shrink	Unsupported shrink and data loss
Candidate data has unknown retention	Stop at inventory and request authority	Destruction of required logs or backups
Remote share may be unavailable at boot	Use `_netdev,nofail` and test `mount -a`	Boot delay or emergency mode

Workflow

Detect distro, mount source, filesystem type, block use, and inode use; stop if the target is ambiguous.
Rank consumers without crossing unrelated mounts, and distinguish deleted-open files from ordinary files.
Select cleanup, growth, swap, or network-mount handling from the decision table; obtain authority before mutation.
Preview destructive candidates and preserve retention-protected data; stop when expected recovery is not measurable.
Apply one bounded change, then verify df, df -i, findmnt, service health, and boot-safe configuration.
If a command fails, preserve current state, record its output, and provide the narrow recovery or rollback step.

Outputs

Artefact	Consumer	Acceptance condition
Storage diagnosis	Incident owner	Names mount, filesystem, block/inode measurements, and ranked cause
Change record	System owner	Lists authorised commands, deleted paths or config diffs, and rollback
Verification snapshot	Operations	Shows post-change capacity plus mount/service checks

Evidence Produced

Artefact	Acceptance
Storage evidence pack	Includes before/after `df`, inode and consumer evidence, filesystem type, authorised commands, applicable `mount -a`, and redacted residual risk

Quality Standards

Measurements identify the affected mount rather than only the directory path.
Every deletion is bounded by path, age or retention rule, and explicit authority.
Network mounts survive an unavailable peer without blocking boot.
Verification proves reclaimed capacity or a correctly mounted target.

Anti-Patterns

Deleting broad directory trees before measuring. Fix: rank consumers on the affected mount first.
Vacuuming journals without checking retention. Fix: obtain the approved time or size boundary.
Treating package-cache cleanup as root-cause analysis. Fix: identify the growth source and recurrence control.
Creating swap on a nearly full filesystem. Fix: verify capacity and persistence requirements first.
Putting an SMB password in /etc/fstab. Fix: use a root-owned 0600 credentials file.
Shrinking XFS in place. Fix: grow it or plan a backed-up migration.

Worked Example

An alert shows /var at 96% while / is healthy. The operator supplies a 14-day journal policy. Measure /var separately, find 18 GiB in journald, vacuum only to the approved boundary, and record before/after df plus journalctl --disk-usage; do not delete application backups discovered on another mount.

References

This skill is self-contained. Every command below is a standard tool on both families (the body shows Debian/Ubuntu; see Distro support above for RHEL-family equivalents). The sk-* scripts in the Optional fast path section are convenience wrappers — never required.

Check Usage

df -h                           # filesystem overview (concern: > 85% used)
df -i                           # inode usage (can be full independently)
du -sh /var/www/* | sort -rh | head -10
du -sh /var/log/* 2>/dev/null | sort -rh | head -10
du -sh ~/backups/* 2>/dev/null | sort -rh | head -5
sudo find / -type f -size +100M 2>/dev/null | head -10

Safe Cleanup (In Order Of Safety)

# 1. APT cache (always safe)
sudo apt clean && sudo apt autoremove

# 2. Journal logs (safe, keeps recent 14 days)
sudo journalctl --vacuum-time=14d
sudo journalctl --vacuum-size=500M

# 3. Old backup files (verify retention script is running first)
find ~/backups/mysql/ -name "*.gpg" -mtime +7 -delete

# 4. Temp files
sudo find /tmp /var/tmp -type f -mtime +7 -delete

# 5. node_modules after successful Astro build
# cd /var/www[/html]/<site> && rm -rf node_modules
# (update-all-repos will reinstall on next pull)

Emergency Disk Full

# Fast identification
df -h && du -sh /var/www/* /var/log/* ~/backups/* 2>/dev/null | sort -rh | head -10

# Immediate wins (safe):
sudo apt clean
sudo journalctl --vacuum-size=200M
sudo find /tmp /var/tmp -type f -mtime +7 -delete

# Truncate an oversize log (safer than deleting):
sudo truncate -s 0 /var/log/<oversize-log-file>

Inode Exhaustion (df -i shows 100%)

# Find dir with most files:
sudo find / -xdev -type f 2>/dev/null | cut -d/ -f2 | sort | uniq -c | sort -rn | head

# Common causes: PHP sessions, mail spool, tiny cache files
sudo find /var/lib/php/sessions/ -type f | wc -l
sudo find /tmp -type f | wc -l

Swapfile (Safety Net For No-Swap Servers)

sudo fallocate -l 2G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab
echo 'vm.swappiness=10' | sudo tee -a /etc/sysctl.d/99-swappiness.conf
sudo sysctl vm.swappiness=10
free -h                   # verify Swap shows 2G

Full cleanup targets and LVM reference: references/storage-reference.md

Network Mounts: NFS And CIFS/SMB

Two network filesystems show up on Linux clients. NFS is the UNIX-native choice (Linux-to-Linux exports, home directories). CIFS/SMB is the Windows/Samba/NAS choice — reach for it when the server is Windows or a NAS exposing SMB. Both are mounted via mount, persist through /etc/fstab or autofs, and use 0 0 for the dump/pass fields.

NFS (Linux-to-Linux)

# Install client: apt install nfs-common   |   dnf install nfs-utils
showmount -e server2                       # list exports
sudo mount -t nfs server2:/share /mnt/nfs  # manual mount

# Persistent (fstab): server:share is colon-separated
# server2:/share  /mnt/nfs  nfs  _netdev,nofail  0  0

CIFS/SMB (Windows / Samba / NAS)

# Install client: apt install cifs-utils smbclient | dnf install cifs-utils samba-client
smbclient -L //192.168.4.200 -U guest      # discover shares (IP avoids DNS issues)

# Manual test mount (prompts for password):
sudo mount -t cifs -o username=linda //server2/sambashare /mnt/share

Never put a password in plaintext in fstab. Use a 0600 credentials file:

sudo tee /root/.smbcredentials >/dev/null <<'EOF'
username=linda
password=SuperSecret
domain=WORKGROUP
EOF
sudo chmod 600 /root/.smbcredentials       # MUST be 0600 — root-only

Persistent CIFS mount in /etc/fstab (note _netdev,nofail so a missing server never blocks boot):

//server2/sambashare  /sambamount  cifs  credentials=/root/.smbcredentials,uid=1000,gid=1000,vers=3.0,_netdev,nofail,x-systemd.automount  0  0

sudo mount -a            # test before rebooting; fails loudly on a typo

On-demand via autofs (mounts on first access, unmounts when idle — works for both NFS and CIFS):

# /etc/auto.master :  /cifs  /etc/auto.cifs  --timeout=60
# /etc/auto.cifs   :  sambashare  -fstype=cifs,credentials=/root/.smbcredentials,vers=3.0  ://server2/sambashare
sudo systemctl enable --now autofs

Quick troubleshooting: error(112)/error(95) → SMB version, try vers=3.0 then vers=2.1 (never 1.0 — insecure). error(13) → credentials or sec= (sec=ntlmssp for username/password, sec=krb5 in an AD/FreeIPA domain). Full detail, ownership mapping, wildcard autofs maps, and the Samba server side: references/cifs-and-network-mounts.md

Optional fast path (when sk-* scripts are installed)

Running sudo install-skills-bin linux-disk-storage installs:

Task	Fast-path script
Mount a CIFS/SMB share (creds + test + fstab)	`sudo sk-cifs-mount //server/share /mnt/share`

These are optional wrappers around the commands above.

Scripts

This skill installs the following scripts to /usr/local/bin/. To install:

sudo install-skills-bin linux-disk-storage

Script	Source	Core?	Purpose
sk-cifs-mount	scripts/sk-cifs-mount.sh	no	Mount a CIFS/SMB (Samba/Windows) share: install `cifs-utils`, build/verify a 0600 credentials file, test-mount, optionally add a persistent `_netdev,nofail` fstab entry.