Levels 35–39: File Editing & Sharing

Level 35: Vim Essentials

Every Linux box has vim, or at least vi. Editing a config over SSH at 3am is not the time to learn modal editing from scratch.

Key / Command	What it does	Why it matters
`vim file`	Open a file	Starts in normal mode, keystrokes are commands
`i`	Enter insert mode	Now you can type text
`Esc`	Back to normal mode	The most-pressed key in vim
`dd`	Delete the current line	`3dd` deletes three lines
`/pattern`	Search forward	`n` repeats, `?` searches backward
`:wq`	Save and quit	`:q!` discards changes instead
`:%s/foo/bar/g`	Replace every occurrence in the file	`%` = every line, `g` = every match per line

Level 36: Advanced Permissions & ACLs

chmod’s owner/group/other model runs out of expressiveness fast.

Command	What it does	Why it matters
`getfacl file`	Show a file’s full ACL	Standard bits plus any extended entries
`setfacl -m u:alice:rw file`	Grant a specific user access	Extra access without changing the owner
`setfacl -m g:devs:rx file`	Grant a specific group access	Same idea, for a whole group
`setfacl -b file`	Strip all extended ACLs	Clean baseline when ACLs have drifted
`umask`	Show the current default-permission mask	Determines new file/dir permissions
`umask 027`	Tighten the umask	New files: 640, new dirs: 750

How a Linux box speaks SMB, so Windows machines see it as a normal network share.

Command	What it does	Why it matters
`testparm`	Validate smb.conf syntax	Test before restarting, a broken restart drops every share
`smbpasswd -a alice`	Set a Samba password for a Linux user	Samba keeps its own separate password database
`systemctl restart smbd`	Apply a config change	Samba doesn’t reread its config automatically
`smbclient -L fileserver -U alice`	List shares from a client	Confirms share name and credentials before mounting
`mount -t cifs //fileserver/data /mnt/win -o username=alice`	Mount a Samba share	`cifs` is the modern SMB client filesystem

The native way Unix and Linux machines share filesystems with each other.

Command	What it does	Why it matters
`exportfs -v`	Show current NFS exports	Reads the live kernel export table
`exportfs -ra`	Apply /etc/exports changes	Re-exports everything without an interruption
`showmount -e 192.168.1.10`	See what a server exports	Check before mounting blind
`mount -t nfs 192.168.1.10:/data /mnt/nfs`	Mount an NFS share	`server:/path` as one argument
`umount /mnt/nfs`	Unmount	`-f` forces it, `-l` does a lazy unmount

Level 39: Sync & Backup with rsync

Only transfers what changed. Runs over SSH with no extra setup. Learn this one properly.

rsync -av home/ /mnt/backup/                    # basic archive copy
rsync -av --delete home/ /mnt/backup/            # mirror exactly, remove extras at destination
rsync -avz -e ssh home/ alice@backup:/data/      # sync over SSH
rsync -avzn home/ /mnt/backup/                   # dry run, preview only
rsync -avz --progress home/ /mnt/backup/         # live progress on a large transfer