# No password for sudo echo "$USER ALL=(ALL:ALL) NOPASSWD: ALL" | sudo tee -a /etc/sudoers # Run the last command as root sudo !! # Just because it's funny alias please='sudo' # ext2/ext3/ext4 file system resizer (e.g. resize EC2 root volume to actual disk size) sudo resize2fs /dev/xvda1 # Mount options for /etc/fstab UUID=<UUID> /home/ec2-user/<some mount path> ext4 defaults,nofail 0 2 # List drives lsblk # List drives by UUID ls -l /dev/disk/by-uuid # Start HTTPD at boot (CentOS) sudo chkconfig --levels 345 httpd on # Mirror site with wget wget -p -r -l4 -E -k -nH <url> # Download all files listed in urls.txt xargs -n 1 curl -O < urls.txt # Move many files (millions of files..) echo *.ext | xargs mv -t <path> # Read large file quickly (faster than "more"); less <file> # View last 100 lines of file tail -100 <file> # Clear contents of file truncate -s 0 <file> # Run programs and summarize system resource usage time nslookup <domain> 8.8.8.8 # Redirect stdout and stderr to log file with timestamps ./some_script.sh 2>&1 | gawk '{ print strftime("[%Y-%m-%d %H:%M:%S]"), $0 }' >> some_script.log # Get User-Agents from nginx logfile cat <file> | grep "GET" | awk -F'"' '{print $6}' | cut -d' ' -f1 | grep -E '^[[:alnum:]]' | sort | uniq -c | sort -rn # Merge multiple files, recursively find . -name "<file>.<ext>" -o -name "<file>*.<ext>" | xargs cat > ./<outputfile> # Get CPU info grep "model name" /proc/cpuinfo # Get number of CPUs grep processor /proc/cpuinfo | wc -l # Get total memory (in MB) awk '/MemTotal/ {printf( "%.2fMB\n", $2 / 1024 )}' /proc/meminfo # Get files over 50MB find <path> -type f -size +50000k -exec ls -lh {} \; | awk '{ print $9 ": " $5 }' # Find file by name and ignore errors find / -name "<name>" 2> /dev/null # Find files containing string grep -Ril "<string>" ./ # SHA 512 sum of file (macOS) openssl dgst -sha512 <file> # MD5 sum of file md5 <file> # ~/.ssh/config example (easily SSH to host with "ssh example") # Host example # Hostname 111.222.333.444 # User ec2-user # IdentityFile ~/.ssh/example.pem # SSH copy from remote host to local (<example> is the Host in ~/.ssh/config) scp example:/some/path/on/remove/server/file.ext localfile.ext # rsync from local to remote host, excluding mac files (<example> is the Host in ~/.ssh/config) rsync -rave "ssh -i /Users/$USER/.ssh/example.pem" --exclude ".DS_Store" -r . example:~/some-directory-here # Last 100 most used commands history | sed "s/^[0-9 ]*//" | sed "s/ *| */\n/g" | awk '{print $1}' | sort | uniq -c | sort -rn | head -n 100 # Determine directory where this script is running from (1) cd ${0%/*} # Determine directory where this script is running from (2) script_dir=$(dirname $(echo $0 | sed -e "s,^\([^/]\),$(pwd)/\1,")) # Clear console in Node.js (*nix) console.log('\033[2J'); # Connect to Cisco ASA devices via USB console cable screen /dev/tty.usbserial-a103xxxxx # List files displaying permissions in octal values (755 drwxr-xr-x, 644 -rw-r--r--) alias lso="ls -alG | awk '{k=0;for(i=0;i<=8;i++)k+=((substr(\$1,i+2,1)~/[rwx]/)*2^(8-i));if(k)printf(\" %0o \",k);print}'" # Sum all numbers in a file using awk awk '{ sum += $1 } END { print sum }' <file> # List all files installed by package (CentOS) rpm -ql <package> # Search for filename containing "options" installed by package "pptpd" (CentOS) rpm -ql pptpd | grep options # Get IP address (Ethernet 0): /sbin/ifconfig eth0 | grep "inet addr" | awk -F: '{print $2}' | awk '{print $1}' # Get IP address (All interfaces): /sbin/ifconfig | grep -B1 "inet addr" | awk '{ if ( $1 == "inet" ) { print $2 } else if ( $2 == "Link" ) { printf "%s:" ,$1 } }' | awk -F: '{ print $1 ": " $3 }' # Send UDP message to a specific host and port using NetCat nc -u <ip> <port> <<< '<message>' # Check if TCP or UDP port is open (/dev/tcp/host/port or /dev/udp/host/port) cat < /dev/tcp/127.0.0.1/22 # Scan for RDP (10.0.1.0 - 10.0.1.255) nmap -p3389 -P0 -sS 10.0.1.0/24 | grep "scan" | cut -d "(" -f2 | cut -d ")" -f1 # ipsec newhostkey hangs: ipsec newhostkey --configdir /etc/ipsec.d --output ~/ipsec.secrets --bits 4096 mv /dev/random /dev/chaos ln -s /dev/urandom /dev/random # Connect to VPN service (macOS) ref: http://superuser.com/questions/358513/start-configured-vpn-from-command-line-osx scutil --nc start <name_of_service> --user <vpn_username> --password <vpn_password> # Monitor pppd log tail -f /var/log/syslog | grep pppd # Bandwidth trottling, enabling 150kB/s on port 80 (removed from recent versions of macOS) sudo ipfw pipe 1 config bw 150KByte/s sudo ipfw add 1 pipe 1 src-port 80 # Bandwidth trottling, disable sudo ipfw delete 1 # Check if MTU size is wrong (fragmented packets) tcpdump -i eth0 -s 1500 port not 22 | strings | grep "frag" # Check current DNS servers used cat /etc/resolv.conf # Google public recursive DNS 8.8.8.8 8.8.4.4 # Quad9 public recursive DNS 9.9.9.9 # Level3 public recursive DNS 4.2.2.1 4.2.2.2 4.2.2.3 4.2.2.4 4.2.2.5 4.2.2.6 # Like top, but for networking (built in macOS) nettop # Like top, but for disk I/O iotop # Like top htop # Disable ecAssessment system policy security (allow unidentified app to be started) sudo spctl --master-disable # Convert PNG image sequence (image-000.png) to H.264 using ffmpeg ffmpeg -i ./image-%03d.png -f mp4 -vcodec libx264 -pix_fmt yuv420p <filename>.mp4 # AWS S3: Get total size and number of files of bucket aws s3 ls s3://<bucket_name> --recursive --human-readable --summarize | grep "Total Size" # SSH login without password ssh-keygen -t rsa -b 2048 -v ssh-copy-id -i ~/.ssh/<cert>.pub <user>@<server-ip> # xenserver start all hosts xe vm-start --multiple