Utilities

pwd

Show the current folder (Print Working Directory).

ls -lah

List files with permissions, sizes and hidden files (-a), human-readable format (-h).

cd /percorso/cartella

Enter a directory. cd .. goes up one level, cd ~ goes to home.

mkdir -p progetto/docs

Create a folder; -p also creates any missing parent folders.

cp -a sorgente/ destinazione/

Copy files or folders preserving permissions and timestamps (-a).

mv vecchio.txt nuovo.txt

Rename or move files and folders.

rm file.txt

Delete a file. rm -r folder/ deletes a folder and its contents.

du -sh * | sort -h

Size of each item in the current folder, sorted smallest first.

df -h

Available disk space on all partitions, human-readable.

chmod 644 file.txt

Set numeric permissions: owner rw, group and others read-only (typical for web files).

chmod 755 script.sh

Owner rwx, others rx — standard for executable scripts and public folders.

chmod -R 775 cartella/

Apply permissions recursively to the entire folder (-R).

chown www-data:www-data file.php

Change file owner and group (Apache/Nginx user on Debian/Ubuntu).

chown -R utente:gruppo cartella/

Change owner recursively on a directory.

ls -l file.txt

Show permissions, owner, group, size and modification date.

ps aux | grep apache

List processes; filter with grep to find Apache ones.

top

Real-time process monitor (CPU, RAM). Exit with q.

htop

Interactive version of top with colour bars and sorting (if installed).

kill -15 PID

Terminate a process gracefully (SIGTERM). Use kill -9 PID only if it does not respond.

systemctl status httpd

Apache service status (httpd on RHEL/CentOS, apache2 on Debian/Ubuntu).

systemctl restart httpd

Restart the web service after configuration or module changes.

systemctl enable --now nome-servizio

Enable the service at boot and start it immediately.

journalctl -u httpd -n 50 --no-pager

Last 50 httpd service logs from the systemd journal.

ping -c 4 google.com

Check host reachability; -c 4 sends 4 packets and stops.

curl -I https://www.fr-italy.com

Show only HTTP response headers (-I), useful for checking redirects and cache.

curl -v https://sito.it/pagina

HTTP request with TLS connection details and headers (-v verbose).

wget -O file.zip https://esempio.it/file.zip

Download a file from a URL and save with the specified name (-O).

dig fr-italy.com A +short

Query DNS for A records; +short shows only the IP.

dig fr-italy.com MX

MX records for the domain (mail servers).

nslookup smtps.aruba.it

Simple DNS resolution of a hostname.

ss -tlnp

Listening TCP ports with associated process (modern alternative to netstat).

traceroute google.com

Path of routers traversed to reach the destination.

openssl s_client -connect smtps.aruba.it:465 -servername smtps.aruba.it

Test SSL/TLS connection to a server (e.g. SMTP on port 465).

ftp ftp.esempio.it

Interactive FTP client: login, ls, get, put, bye. Prefer SFTP/SCP for security.

lftp -u utente,password ftp://ftp.esempio.it/

Advanced FTP client with mirror, resume and script support (-c). Useful for folder sync.

curl -u utente:password ftp://ftp.esempio.it/file.zip -o file.zip

Download a file via FTP with authentication (-u user:password).

wget ftp://utente:password@ftp.esempio.it/backup.tar.gz

FTP download with credentials in the URL (warning: they appear in shell history).

sftp utente@server.esempio.it

Interactive SFTP session over SSH: ls, cd, get, put, rm.

sftp -i ~/.ssh/chiave.pem utente@server.esempio.it

SFTP authenticated with private key (-i) instead of password.

nmap server.esempio.it

Scan default TCP ports and detect active hosts on the target.

nmap -p 22,80,443,3306,8080 server.esempio.it

Scan only the specified ports (-p), e.g. SSH, HTTP, HTTPS, MySQL.

nmap -sV -p 80,443 server.esempio.it

Detect service versions (-sV) on the specified ports.

nmap -Pn server.esempio.it

Skip initial ping (-Pn): useful when ICMP is blocked by the firewall.

nmap 192.168.1.0/24

Scan all active hosts in a CIDR subnet.

nmap --top-ports 100 -T4 server.esempio.it

Scan the 100 most common ports with faster timing (-T4).

nc -zv server.esempio.it 443

Test whether a TCP port is open (-zv: verbose, zero I/O). Fast alternative to telnet.

nc -zv server.esempio.it 20-25

Check a range of TCP ports (e.g. 20-25 for FTP/SMTP).

telnet server.esempio.it 25

Plain-text TCP connection to a port (e.g. 25 for SMTP banner). Exit with Ctrl+] then quit.

timeout 5 bash -c "echo | telnet server.esempio.it 80"

Quick port 80 test with timeout; useful to verify the service responds.

mysql -h localhost -u webuser -p nome_database

MySQL/MariaDB client: interactive connection to remote or local database (-p prompts for password).

psql -h localhost -U utente -d nome_database

Interactive PostgreSQL client (-h host, -U user, -d database).

redis-cli -h 127.0.0.1 -p 6379 ping

Test Redis connection with PING command (responds PONG if active).

ssh -L 8080:localhost:80 utente@server.esempio.it

Local port forwarding (-L): access a remote service via SSH tunnel (e.g. web on 8080).

ssh -D 1080 utente@server.esempio.it

Dynamic SOCKS proxy (-D) on localhost to route traffic via SSH.

grep "testo" file.log

Search for a string in a single file; prints lines containing the match.

grep -n "errore" file.log

Show line number (-n) next to each occurrence.

grep -i "warning" file.log

Case-insensitive search (-i).

grep -v "DEBUG" file.log

Invert match (-v): show lines that do NOT contain the string.

grep -w "error" file.log

Match whole words only (-w), not substrings (e.g. will not match "terror").

grep -c "404" access.log

Count lines containing the match (-c), without printing the text.

grep -l "mysql" *.php

List only filenames (-l) that contain the string.

grep -L "TODO" *.php

List files (-L) that do NOT contain the string.

grep -r "sendemail" /var/www/html/

Search recursively (-r) in all files under a folder.

grep -R "config" /etc/

Recursive search following symbolic links too (-R).

grep -rn --color=always "function " .

Recursive with line numbers (-n) and colour highlighting in the current folder (.).

grep -E "error|warning|fatal" file.log

Extended regex (-E): match multiple patterns separated by | (OR).

grep -A 3 "Exception" file.log

Print 3 lines after (-A) each match — useful for stack traces.

grep -B 2 "Fatal" file.log

Print 2 lines before (-B) each match.

grep -C 5 "SMTP connect" file.log

Context (-C): 5 lines before and after each occurrence.

grep --include="*.php" -r "dbquery" .

Search only in files with the specified extension (--include).

grep --include="*.{php,tpl,js}" -r "smarty" .

Multiple extensions at once using curly braces.

grep --exclude-dir=vendor --exclude-dir=node_modules -r "class " .

Exclude folders (--exclude-dir) from recursive search.

grep -r "password" . 2>/dev/null

Redirect permission errors to /dev/null to keep output clean.

zgrep "errore" /var/log/syslog.1.gz

Search inside compressed log files (.gz) without extracting them manually.

tail -n 50 file.log

Last 50 lines of the file (-n = number of lines).

tail -n 100 /var/log/httpd/error_log

Read the last 100 lines of an Apache log (RHEL/CentOS path).

tail -n +50 file.log

From line 50 to the end (+N = starting from line N, inclusive).

head -n 20 file.log

First 20 lines of the file.

head -n -10 file.log

Entire file except the last 10 lines (-N negative).

head -c 500 file.bin

First 500 bytes (-c) — useful for inspecting binary or CSV files.

tail -f /var/log/httpd/error_log

Follow the file in real time (-f follow): new lines appear as they arrive.

tail -F /var/log/apache2/error.log

Like -f but reopens the file if rotated/recreated (-F, useful with logrotate).

tail -f access.log error.log

Follow multiple files at once; each line is prefixed with the filename.

tail -f error_log | grep --line-buffered "PHP"

Filter live only PHP lines (--line-buffered avoids pipe delays).

tail -f error_log | grep -i "error\|fatal\|warning"

Live monitor filtering errors, fatal and warning messages.

tail -n 200 error_log | grep "sendemail"

Search in the last 200 lines (very common tail + grep combination).

less +F /var/log/httpd/error_log

Open less in follow mode (like tail -f); Ctrl+C to exit follow, q to close.

find . -name "*.php"

Find files by name in the current folder and subfolders.

find . -iname "*.PHP"

Like -name but case-insensitive (-iname).

find /var/www -type f -name "*.log"

-type f limits to files (d = directories only, l = links).

find . -type d -name "cache"

Search directories only (-type d) with that name.

find . -maxdepth 2 -name "*.tpl"

Limit depth (-maxdepth 2 = current + one level below).

find . -mindepth 1 -maxdepth 1 -type f

Files in the current folder only, no subfolders.

find /var/www -mtime -7

Modified in the last 7 days (-mtime -N, whole days).

find /var/www -mtime +30

Modified more than 30 days ago (+N).

find . -mmin -60

Modified in the last 60 minutes (-mmin, more precise than -mtime).

find . -newer file_riferimento.txt

Files newer than another file (-newer).

find . -size +10M

Files larger than 10 megabytes (+size).

find . -size -100k

Files smaller than 100 kilobytes.

find . -empty -type f

Empty files (0 bytes).

find . -perm 0777 -type f

Files with exact permissions 0777 (warning: security risk).

find . -user www-data

Files owned by the specified user.

find . ! -path "./vendor/*" -name "*.php"

Exclude a path with ! -path (e.g. skip vendor).

find . -name "*.php" -exec grep -l "mysql" {} \;

Among .php files found, list those containing "mysql" (-exec + grep -l).

find . -name "*.php" -print0 | xargs -0 grep -l "PDO"

Safe variant with filenames containing spaces (-print0 | xargs -0).

find . -name "*.bak" -delete

Find and delete (-delete) matching files — use with caution.

find . -name "*.tmp" -mtime +7 -exec rm {} \;

Delete .tmp files older than 7 days with -exec rm.

cat file.log

Print the entire contents of a file to the terminal.

less /var/log/httpd/error_log

Open a long file with scrolling; /text searches, n/N next/previous, q exits.

sed -n "10,25p" file.log

Print only lines 10 through 25 (range extraction).

awk '/error/ {print}' file.log

Print lines containing "error" (simple awk filter).

awk -F: '{print $1}' /etc/passwd

Use : as separator (-F) and print the first field of each line.

wc -l file.txt

Count lines (-l), words and bytes of a file.

wc -l $(find . -name "*.php")

Count total lines summing all PHP files found.

sort file.txt | uniq -c | sort -rn

Sort lines, count duplicates (uniq -c) and sort by frequency.

cut -d: -f1,3 /etc/passwd

Extract fields 1 and 3 using : as delimiter (-d).

tar -czvf backup.tar.gz cartella/

Create gzip-compressed archive: c=create, z=gzip, v=verbose, f=file.

tar -xzvf backup.tar.gz

Extract a .tar.gz archive into the current folder.

tar -xzvf backup.tar.gz -C /destinazione/

Extract into a specific folder (-C).

zip -r archivio.zip cartella/

Create a recursive zip of a directory.

unzip archivio.zip -d cartella_dest/

Extract a zip into the specified folder.

git status

Modified files, staged changes and current branch.

git diff

Unstaged differences compared to the last commit.

git log --oneline -10

Last 10 commits, one line each.

git pull origin main

Download and merge changes from remote on the main branch.

git add file.php && git commit -m "Messaggio"

Add a file and create a commit with a message.

git checkout -- file.php

Discard uncommitted local changes on a file.

git stash && git stash pop

Temporarily set aside changes and restore them later.

ssh utente@server.example.com

Interactive SSH connection to the remote server.

ssh -i ~/.ssh/chiave.pem utente@host

Connection with a specific private key (-i).

scp file.zip utente@host:/percorso/remoto/

Copy a local file to the server via SSH.

scp -r cartella/ utente@host:/percorso/

Recursive copy of a folder to the server (-r).

rsync -avz --delete sorgente/ host:/dest/

Sync folders via SSH; -a preserves permissions, -v verbose, -z compresses.

ssh-keygen -t ed25519 -C "email@esempio.it"

Generate a new SSH key pair (ed25519 recommended).

php -l file.php

Check PHP syntax without executing the file.

php -v

PHP version installed from the command line.

apachectl configtest

Verify Apache configuration syntax before restart.

httpd -t

RHEL/CentOS equivalent for testing Apache configuration.

tail -f /var/log/httpd/error_log

Monitor Apache errors in real time (typical path on RHEL).

tail -f /var/log/apache2/error.log

Apache error log on Debian/Ubuntu.

grep -i "fatal\|error" /var/log/httpd/error_log | tail -30

Last error/fatal lines in the Apache log.

find . -name "*.php" -exec php -l {} \; | grep -v "No syntax"

Check syntax of all PHP files in the project.

uname -a

Kernel, architecture and operating system version.

free -h

Available and used RAM and swap.

uptime

Server uptime and load average.

whoami && id

Current user and UID/GID with associated groups.

sudo comando

Run a command with root privileges (if authorised).

apt update && apt upgrade -y

Update package list and install updates on Debian/Ubuntu.

dnf update -y

Update packages on Fedora/RHEL 8+.

crontab -l

List cron jobs for the current user.

crontab -e

Edit the user crontab (default editor).

history | tail -20

Last 20 commands run in the current session.