| Command | Description | |
| • | grep . /proc/sys/net/ipv4/* | List the contents of flag files |
| • | set | grep $USER | Search current environment |
| • | tr '\0' '\n' < /proc/$$/environ | Display the startup environment for any process |
| • | echo $PATH | tr : '\n' | Display the $PATH one per line |
| • | kill -0 $$ && echo process exists and can accept signals | Check for the existence of a process (pid) |
| • | find /etc -readable | xargs less -K -p'*ntp' -j $((${LINES:-25}/2)) | Search paths and data with full context. Use n to iterate |
| • | namei -l ~/.ssh | Output attributes for all directories leading to a file name |
| Low impact admin | ||
| # | apt-get install "package" -o Acquire::http::Dl-Limit=42 \ -o Acquire::Queue-mode=access | Rate limit apt-get to 42KB/s |
| echo 'wget url' | at 01:00 | Download url at 1AM to current dir | |
| # | apache2ctl configtest && apache2ctl graceful | Restart apache if config is OK |
| • | nice openssl speed sha1 | Run a low priority command (openssl benchmark) |
| • | chrt -i 0 openssl speed sha1 | Run a low priority command (more effective than nice) |
| • | renice 19 -p $$; ionice -c3 -p $$ | Make shell (script) low priority. Use for non interactive tasks |
| Interactive monitoring | ||
| • | watch -t -n1 uptime | Clock with system load |
| • | htop -d 5 | Better top (scrollable, tree view, lsof/strace integration, ...) |
| • | iotop | What's doing I/O |
| # | watch -d -n30 "nice ps_mem.py | tail -n $((${LINES:-12}-2))" | What's using RAM |
| # | iftop | What's using the network. See also iptraf |
| # | mtr www.pixelbeat.org | ping and traceroute combined |
| Useful utilities | ||
| • | pv < /dev/zero > /dev/null | Progress Viewer for data copying from files and pipes |
| • | wkhtmltopdf http://.../linux_commands.html linux_commands.pdf | Make a pdf of a web page |
| • | timeout 1 sleep inf | run a command with bounded time. See also timeout |
| Networking | ||
| • | python -m SimpleHTTPServer | Serve current directory tree at http://$HOSTNAME:8000/ |
| • | openssl s_client -connect www.google.com:443 </dev/null 2>&0 | openssl x509 -dates -noout | Display the date range for a site's certs |
| • | curl -I www.pixelbeat.org | Display the server headers for a web site |
| # | lsof -i tcp:80 | What's using port 80 |
| # | httpd -S | Display a list of apache virtual hosts |
| • | vim scp://user@remote//path/to/file | Edit remote file using local vim. Good for high latency links |
| • | curl -s http://www.pixelbeat.org/pixelbeat.asc | gpg --import | Import a gpg key from the web |
| • | tc qdisc add dev lo root handle 1:0 netem delay 20msec | Add 20ms latency to loopback device (for testing) |
| • | tc qdisc del dev lo root | Remove latency added above |
| Notification | ||
| • | echo "DISPLAY=$DISPLAY xmessage cooker" | at "NOW +30min" | Popup reminder |
| • | notify-send "subject" "message" | Display a gnome popup notification |
| echo "mail -s 'go home' P@draigBrady.com < /dev/null" | at 17:30 | Email reminder | |
| uuencode file name | mail -s subject P@draigBrady.com | Send a file via email | |
| ansi2html.sh | mail -a "Content-Type: text/html" P@draigBrady.com | Send/Generate HTML email | |
| Better default settings (useful in your .bashrc) | ||
| # | tail -s.1 -f /var/log/messages | Display file additions more responsively |
| • | seq 100 | tail -n $((${LINES:-12}-2)) | Display as many lines as possible without scrolling |
| # | tcpdump -s0 | Capture full network packets |
| Useful functions/aliases (useful in your .bashrc) | ||
| • | md () { mkdir -p "$1" && cd "$1"; } | Change to a new directory |
| • | strerror() { python -c "import os; print os.strerror($1)"; } | Display the meaning of an errno |
| • | plot() { { echo 'plot "-"' "$@"; cat; } | gnuplot -persist; } | Plot stdin. (e.g: • seq 1000 | sed 's/.*/s(&)/' | bc -l | plot) |
| • | hili() { e="$1"; shift; grep --col=always -Eih "$e|$" "$@"; } | highlight occurences of expr. (e.g: • env | hili $USER) |
| • | alias hd='od -Ax -tx1z -v' | Hexdump. (usage e.g.: • hd /proc/self/cmdline | less) |
| • | alias realpath='readlink -f' | Canonicalize path. (usage e.g.: • realpath ~/../$USER) |
| • | ord() { printf "0x%x\n" "'$1"; } | shell version of the ord() function |
| • | chr() { printf $(printf '\\%03o\\n' "$1"); } | shell version of the chr() function |
| Multimedia | ||
| • | DISPLAY=:0.0 import -window root orig.png | Take a (remote) screenshot |
| • | convert -filter catrom -resize '600x>' orig.png 600px_wide.png | Shrink to width, computer gen images or screenshots |
| mplayer -ao pcm -vo null -vc dummy /tmp/Flash* | Extract audio from flash video to audiodump.wav | |
| ffmpeg -i filename.avi | Display info about multimedia file | |
| • | ffmpeg -f x11grab -s xga -r 25 -i :0 -sameq demo.mpg | Capture video of an X display |
| DVD | ||
| for i in $(seq 9); do ffmpeg -i $i.avi -target pal-dvd $i.mpg; done | Convert video to the correct encoding and aspect for DVD | |
| dvdauthor -odvd -t -v "pal,4:3,720xfull" *.mpg;dvdauthor -odvd -T | Build DVD file system. Use 16:9 for widescreen input | |
| growisofs -dvd-compat -Z /dev/dvd -dvd-video dvd | Burn DVD file system to disc | |
| Unicode | ||
| • | python -c "import unicodedata as u; print u.name(unichr(0x2028))" | Lookup a unicode character |
| • | uconv -f utf8 -t utf8 -x nfc | Normalize combining characters |
| • | printf '\300\200' | iconv -futf8 -tutf8 >/dev/null | Validate UTF-8 |
| • | printf 'ŨTF8\n' | LANG=C grep --color=always '[^ -~]\+' | Highlight non printable ASCII chars in UTF-8 |
| • | fc-match -s "sans:lang=zh" | List font match order for language and style |
| Development | ||
| • | gcc -march=native -E -v -</dev/null 2>&1|sed -n 's/.*-mar/-mar/p' | Show autodetected gcc tuning params. See also gcccpuopt |
| • | for i in $(seq 4); do { [ $i = 1 ] && wget http://url.ie/6lko -qO-|| ./a.out; } | tee /dev/tty | gcc -xc - 2>/dev/null; done | Compile and execute C code from stdin |
| • | cpp -dM /dev/null | Show all predefined macros |
| • | echo "#include <features.h>" | cpp -dN | grep "#define __USE_" | Show all glibc feature macros |
| gdb -tui | Debug showing source code context in separate windows | |
| udev | ||
| • | udevadm info -a -p $(udevadm info -q path -n /dev/input/mouse0) | List udev attributes of a device, for matching rules etc. |
| • | udevadm test /sys/class/input/mouse0 | See how udev rules are applied for a device |
| # | udevadm control --reload-rules | Reload udev rules after modification |
| Extended Attributes (Note you may need to (re)mount with "acl" or "user_xattr" options) | ||
| • | getfacl . | Show ACLs for file |
| • | setfacl -m u:nobody:r . | Allow a specific user to read file |
| • | setfacl -x u:nobody . | Delete a specific user's rights to file |
| setfacl --default -m group:users:rw- dir/ | Set umask for a for a specific dir | |
| getcap file | Show capabilities for a program | |
| setcap cap_net_raw+ep your_gtk_prog | Allow gtk program raw access to network | |
| • | stat -c%C . | Show SELinux context for file |
| chcon ... file | Set SELinux context for file (see also restorecon) | |
| • | getfattr -m- -d . | Show all extended attributes (includes selinux,acls,...) |
| • | setfattr -n "user.foo" -v "bar" . | Set arbitrary user attributes |
| BASH specific | ||
| • | echo 123 | tee >(tr 1 a) | tr 1 b | Split data to 2 commands (using process substitution) |
| meld local_file <(ssh host cat remote_file) | Compare a local and remote file (using process substitution) | |
| Multicore | ||
| • | taskset -c 0 nproc | Restrict a command to certain processors |
| • | find -type f -print0 | xargs -r0 -P$(nproc) -n10 md5sum | Process files in parallel over available processors |
| sort -m <(sort data1) <(sort data2) >data.sorted | Sort separate data files over 2 processors | |
© May 30 2010