2025/02/16

Topic 712: Storage Devices and BSD Filesystems

This topic covers partitioning and disk labels, creating and maintaining file systems, mounting and unmounting, managing file permissions, using links, and finding files. Understanding these fundamentals is crucial for effective BSD system administration.

712.1: BSD Partitioning and Disk Labels

fdisk manages MBR (legacy).
disklabel (or bsdlabel) manages BSD labels.
GPT-based systems often use gpart (FreeBSD).

gpart show           # Show partitions
disklabel -E sd0     # OpenBSD: edit disklabel on sd0
installboot          # Install bootstrap on a disk

Note on partition types

MBR (Master Boot Record): Traditional partitioning, often limited to 4 primary partitions.
GPT (GUID Partition Table): Modern scheme with a larger partition limit and better data redundancy.
BSD label: Overlay inside one of these partitions to carve out additional BSD-specific partitions.

712.2: Create File Systems and Maintain Their Integrity

UFS Examples

newfs /dev/ada0p2     # Create UFS on FreeBSD
fsck -y /dev/ada0p2   # Check and repair

df -h                 # Disk usage
du -sh /home          # Show usage of /home

ZFS Examples (FreeBSD, NetBSD)

zpool create mypool /dev/ada1   # Create ZFS pool
zpool status                    # Check pool status
zfs snapshot mypool/usr@backup  # Create snapshot

Tip: ZFS on NetBSD

NetBSD supports ZFS but might require additional configuration or kernel options depending on release. Always consult official documentation for compatibility.

712.3: Control Mounting and Unmounting of File Systems

View all currently mounted filesystems:
```
mount
```
Mount UFS:
```
mount -t ufs /dev/ada0p2 /mnt
```
Unmount:
```
umount /mnt
```
/etc/fstab example:
```
/dev/ada0p2 /usr ufs rw 2 2
```

ZFS Mounts

zfs mount mypool/usr      # Mount a ZFS filesystem
zfs unmount mypool/usr    # Unmount a ZFS filesystem

Note on mount options

Common flags include rw (read-write), ro (read-only), and others like noexec, nodev, etc.
Some BSD flavors might have slight variations in how UFS is referenced (e.g., ufs, ffs).

712.4: Manage File Permissions and Ownership

View permissions:
```
ls -l file.txt
```
Change permissions (symbolic):
```
chmod u+x file.txt
```
Change permissions (octal):
```
chmod 755 file.txt
```

Change owner/group:

chown user file.txt
chgrp group file.txt

umask:
```
umask 022
```

SUID, SGID, and sticky bit

SUID: chmod u+s file executes with the owner’s privileges.
SGID: chmod g+s dir can affect group permissions on directories.
Sticky Bit: chmod +t dir used on /tmp to prevent users from deleting each other’s files.

712.5: Create and Change Hard and Symbolic Links

Hard link:
```
ln original.txt hardlink.txt
```
Symbolic link:
```
ln -s original.txt symlink.txt
```
Remove link:
```
rm symlink.txt
```

Hard vs. soft links

Hard link: Points to the same inode as the original file. Not valid across different filesystems or for directories (on most BSDs).
Symbolic (soft) link: References a path. Can cross filesystems but breaks if the target is moved.

712.6: Find Files and BSD Directory Layout

find / -name httpd.conf
find /var/log -type f -size +10M
find /home -mtime -1

locate config.php
locate.updatedb

whereis python
which sshd

hier(7): The manual page for the BSD filesystem hierarchy (e.g., /bin, /usr, /usr/local, etc.).

Tips on searching

find /path -exec command {} \; can run commands on found items.
-ls prints detailed attributes for each found file.
locate relies on a periodically updated database, so run locate.updatedb if needed.

Cristian Souza