Commands using head (314)

  • Find the 10 users that take up the most disk space

    In OSX you would have to make sure that you "sudo -s" your way to happiness since it will give a few "Permission denied" errors before finally spitting out the results. In OSX the directory structure has to start with the "Users" Directory then it will recursively perform the operation. Your Lord and master, Mematron Show Sample Output


    1
    sudo -s du -sm /Users/* | sort -nr | head -n 10
    mematron · 2012-09-13 10:15:23 4
  • True Random Dice Roll


    1
    echo $(</dev/urandom tr -dc 1-6 | head -c1)
    unixmonkey40000 · 2012-09-21 08:38:51 7
  • Generate a 18 character password, print the password and sha512 salted hash

    Generate a 18 character password from character set a-zA-Z0-9 from /dev/urandom, pipe the output to Python which prints the password on standard out and in crypt sha512 form. Show Sample Output


    1
    cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 18 | head -1 | python -c "import sys,crypt; stdin=sys.stdin.readline().rstrip('\n'); print stdin;print crypt.crypt(stdin)"
    cnyg · 2012-11-09 00:40:22 4
  • generate 30 x 30 matrix

    Replaces hexdump with the more succint xxd, and the sed was unnecessarily complex.


    1
    xxd -p /dev/urandom |fold -60|head -30|sed 's/\(..\)/\1 /g'
    psifertex · 2013-02-19 22:18:52 4
  • Generate password


    1
    tr -dc 'A-Za-z0-9!@#$%^&*' < /dev/urandom | fold -w 12 | head -n 1
    opexxx · 2013-03-15 13:20:32 81
  • Display 16 largest installed RPMs in size order, largest first

    Interesting to see which packages are larger than the kernel package. Useful to understand which RPMs might be candidates to remove if drive space is restricted. Show Sample Output


    1
    rpm -qa --queryformat '%{size} %{name}-%{version}-%{release}\n' | sort -k 1,1 -rn | nl | head -16
    mpb · 2013-03-19 21:10:54 6
  • most used unix commands


    1
    awk '{print $1}' ~/.bash_history | sort | uniq -c | sort -rn | head -n 10
    nesses · 2013-05-03 16:24:30 6
  • Get IP address from domain

    I'm not sure how reliable this command is, but it works for my needs. Here's also a variant using grep. nslookup www.example.com | grep "^Address: " | awk '{print $2}' Show Sample Output


    1
    nslookup www.example.com | tail -2 | head -1 | awk '{print $2}'
    wsams · 2013-09-05 20:26:45 11
  • Prints the latest modified files in a directory tree recursively

    Sorts by latest modified files by looking to current directory and all subdirectories Show Sample Output


    1
    find . -name '*pdf*' -print0 | xargs -0 ls -lt | head -20
    fuats · 2013-10-03 21:58:51 9
  • Create a bunch of dummy text files


    1
    for i in `seq 1 4096`; do tr -dc A-Za-z0-9 </dev/urandom | head -c8192 > dummy$i.rnd; done
    BoxingOctopus · 2013-11-11 21:27:15 8
  • Create a bunch of dummy text files

    Using the 'time' command, running this with 'tr' took 28 seconds (and change) each time but using base64 only took 8 seconds (and change). If the file doesn't have to be viewable, pulling straight from urandom with head only took 6 seconds (and change)


    1
    for i in {1..4096}; do base64 /dev/urandom | head -c 8192 > dummy$i.rnd ; done
    pdxdoughnut · 2013-11-12 00:36:10 9
  • Download latest NVIDIA Geforce x64 Windows driver

    Download latest NVIDIA Geforce x64 Windows7-8 driver from Nvidia's website. Pulls the latest download version (which includes beta). This is the "English" version. The following command includes a 'sed' line to replace "english" with "international" if needed. You can also replace the starting subdomain with "eu." "uk." and others. Enjoy this one liner! 1 character under the max :) wget "us.download.nvidia.com$(wget -qO- "$(wget -qO- "nvidia.com/Download/processFind.aspx?psid=95&pfid=695&osid=19&lid=1&lang=en-us" | awk '/driverResults.aspx/ {print $4}' | cut -d "'" -f2 | head -n 1)" | awk '/url=/ {print $2}' | sed -e "s/english/international/" | cut -d '=' -f3 | cut -d '&' -f1)" Show Sample Output


    1
    wget "us.download.nvidia.com$(wget -qO- "$(wget -qO- "nvidia.com/Download/processFind.aspx?psid=95&pfid=695&osid=19&lid=1&lang=en-us"|awk '/driverResults.aspx/ {print $4}'|cut -d "'" -f2|head -n 1)"|awk '/url=/ {print $2}'|cut -d '=' -f3|cut -d '&' -f1)"
    lowjax · 2013-11-21 03:04:59 11
  • Find last reboot time

    Specific to OSX. Show Sample Output


    1
    sysctl -a | grep boottime | head -n 1
    lgarron · 2014-01-24 13:03:48 7
  • Find 10 largest files in git history


    1
    git verify-pack -v .git/objects/pack/pack-*.idx | grep blob | sort -k3nr | head | while read s x b x; do git rev-list --all --objects | grep $s | awk '{print "'"$b"'",$0;}'; done
    qdrizh · 2014-06-25 07:37:24 6
  • Print the IP address and the Mac address in the same line

    Print the IP address and the Mac address in the same line Show Sample Output


    1
    ifconfig | head -n 2 | tr -d '\n' | sed -n 's/.*\(00:[^ ]*\).*\(adr:[^ ]*\).*/mac:\1 - \2/p'
    Koobiac · 2014-09-03 14:35:27 18
  • Top 30 History

    Top 30 History Command line with histogram display Show Sample Output


    1
    history|awk '{print $2}'|sort|uniq -c|sort -rn|head -30|awk '!max{max=$1;}{r="";i=s=100*$1/max;while(i-->0)r=r"#";printf "%50s %5d %s %s",$2,$1,r,"\n";}'
    injez · 2014-09-29 12:40:43 9
  • Monitor system load and print out top offending processes

    This checks the system load every second and if it's over a certain threshold (.8 in this example), it spits out the date, system loads and top 4 processes sorted by CPU. Additionally, the \a in the first echo creates an audible bell.


    1
    while sleep 1; do if [ $(echo "$(cat /proc/loadavg | cut -d' ' -f1) > .8 " | bc) -gt 0 ]; then echo -e "\n\a"$(date)" \e[5m"$(cat /proc/loadavg)"\e[0m"; ps aux --sort=-%cpu|head -n 5; fi; done
    tyzbit · 2014-12-08 15:44:40 8
  • Find the date of the first commit in a git repository

    Finds the date of the first commit in a git repository branch Show Sample Output


    1
    git rev-list --all|tail -n1|xargs git show|grep -v diff|head -n1|cut -f1-3 -d' '
    binaryten · 2015-02-04 19:35:16 11
  • Most used commands from history (without perl)

    I copied this (let's be honest) somewhere on internet and I just made it as a function ready to be used as alias. It shows the 10 most used commands from history. This seems to be just another "most used commands from history", but hey.. this is a function!!! :D Show Sample Output


    1
    mosth() { history | awk '{CMD[$2]++;count++;}END { for (a in CMD)print CMD[a] " " CMD[a]/count*100 "% " a;}' | grep -v "./" | column -c3 -s " " -t | sort -nr | nl | head -n10; }
    nnsense · 2015-05-11 17:41:55 19
  • Printout a list of field numbers (awk index) from a CSV file with headers as first line.

    Useful to identify the field number in big CSV files with large number of fields. The index is the reference to use in processing with commands like 'cut' or 'awk' involved. Show Sample Output


    1
    head -1 file.csv | tr ',' '\n' | tr -d " " | awk '{print NR,$0}'
    neomefistox · 2015-08-26 05:46:15 18
  • Grab the top 5 CLFUContest one-liners


    1
    curl -sL http://goo.gl/3sA3iW | head -16 | tail -14
    cadejscroggins · 2015-09-19 07:19:49 10
  • Get AWS temporary credentials ready to export based on a MFA virtual appliance

    You might want to secure your AWS operations requiring to use a MFA token. But then to use API or tools, you need to pass credentials generated with a MFA token. This commands asks you for the MFA code and retrieves these credentials using AWS Cli. To print the exports, you can use: `awk '{ print "export AWS_ACCESS_KEY_ID=\"" $1 "\"\n" "export AWS_SECRET_ACCESS_KEY=\"" $2 "\"\n" "export AWS_SESSION_TOKEN=\"" $3 "\"" }'` You must adapt the command line to include: * $MFA_IDis ARN of the virtual MFA or serial number of the physical one * TTL for the credentials Show Sample Output


    1
    head -n1 | xargs -I {} aws sts get-session-token --serial-number $MFA_ID --duration-seconds 900 --token-code {} --output text --query [Credentials.AccessKeyId,Credentials.SecretAccessKey,Credentials.SessionToken]
    keymon · 2016-04-12 10:57:00 46
  • Find top 10 largest files


    1
    du -a /var | sort -n -r | head -n 10
    zluyuer · 2016-05-27 04:05:08 12
  • Read random news on the internet

    sort -R randomize the list. head -n1 takes the first.


    1
    links `lynx -dump -listonly "http://news.google.com" | grep -Eo "(http|https)://[a-zA-Z0-9./?=_-]*" | grep -v "google.com" | sort -R | uniq | head -n1`
    mogoh · 2016-07-26 12:54:53 15
  • Find last 50 modified files


    1
    find / -path /proc -prune -o -type f -printf '%TY-%Tm-%Td %TT %p\n' | sort -r | head -50
    sidneycrestani · 2016-11-20 02:45:01 13
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Check for login failures and summarize
This command checks for the number of times when someone has tried to login to your server and failed. If there are a lot, then that user is being targeted on your system and you might want to make sure that user either has remote logins disabled, or has a strong password, or both. If your output has an "invalid" line, it is a summary of all logins from users that don't exist on your system.

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Equivalent to ifconfig -a in HPUX
not shown ifconfig error

execute a command in case of success or execute a command in case of failure

Loop over the days of a month, in $YYYY$MM$DD format
Edit YYYY and MM at the beginning of the command with the year and month you want. Note that `DD=$(printf "%02d" $d)` will pad single digit integers with a leading zero. Substitute `echo $YYYY$MM$DD` at the end of the line with the command you want to launch, for instance script.pl --yyyymmdd $YYYY$MM$DD Also available on GitHub as bash util: https://github.com/fibo/yyyymmdd

Check disk for bad sectors
Checks HDD for bad sectors, just like scandisk or chkdisk under some other operating system ;-).

Calculate days on which Friday the 13th occurs (inspired from the work of the user justsomeguy)
Friday is the 5th day of the week, monday is the 1st. Output may be affected by locale.

Bash command to convert IP addresses into their "reverse" form

ttyS0 - terminal on serial connection
I actually planned to do this for quite a long time, but since I haven't had any suitable client hardware, I procrastinated this. Now, the old laptop I've got from my dad, features an RS-232 port. So, now that I had technically a client, that I could test my RS-232 connection with, I ordered a null modem cable. There is no RS-232 outlet on my desktop computer directly on the mainboard, but theres a connector on the mainbord, where a RS-232 outlet can be attached to. The outlet will then cover up a PCI slot. # Activating RS-232 Ok, once all cables were in place, I tried to access both RS-232 ports by reading from them directly. They're usually ttyS0 or ttyS1, depending what COM-Port it is. From the file /proc/tty/driver/serial, information about the serial setup can be obtained. A setserial -q /dev/ttyS0 might be usefull as well. Usually, the UART Type is 16550A, on a standard PC. Mine wasn't working though. At leas not right from the start, when I tried to read the interface with cat /dev/ttyS0 I got the following error: # cat /dev/ttyS0 cat: /dev/ttyS0: Input/output error Obviously, the driver couldn't activate the hardware. Reason was, it was deactivated in BIOS. After activating RS-232 there, it worked well. As a last action, I added myself to the uucp group, so I have user permission to the serial lines. It is not necessary for the terminal setup, but a good idea to do so, just for future projects, maybe... # Setting up a terminal Once the Serial line is configured and working properly, it's time to let a terminal run on that port. This is what I added to my /etc/inittab : s0:2345:respawn:/sbin/agetty -L 38400 ttyS0 I added it quite on the top of that file, right below the 'si' statement, mingetty cannot be used for serial connections, it cannot be run in a console, too. I tried it for testing purposes, but the cosole - along with your login program - will log you out, as soon as you log in over your serial line. '-L' means this is a local line, with no carrier signal. 38400 is the standard speed of a Linux console, it might be a bit high, I was told, but it works well. I tested that with some higher values as well (115200) and it worked too, I guess it tepends on things like cable length, etc. Last parameter, is the serial tty to listen on. The terminal type can be specified as an additional parameter at the end of the parameter list, vt102, for instance. This is sometimes required, depending on the client. After finishing editing /etc/inittab, an init q will make the system re-read /etc/inittab and apply changes. The agetty should now be listening on ttyS0. #Setting up a client It's time to establish a connection and test the serial line. I use a laptop, that has an RS-232 port, so some preliminary setup is required. I tried minicom as terminal initially, but it turned out, not to be the best client. It initializes the modem, this lasts quite long, and it doesn't convey ANSI colors. So the better option is cu, it's part of the UUCP-Package. Oh, and the serial port of that computer, has to be accessible as well, of course. Once everything was set up, I established the connection: $ cu -l ttyS0 -38400 --nostop Pretty self explanatory, I think. The --nostop option disables XON/XOFF handling. # root access over ttyS0 In order to become root over the serial terminal, the tty needs to be added to /etc/securetty I appended ttyS0 to the end of the file. It is now possible, to gain root access over the serial terminal. The agetty process needs to be restarted to apply changes. # Accessing GRUB over ttyS0 To make bootloader access possible over ttyS0, some changes to /boot/grub/menu.lst need to be done. (GRUB is the bootloader I use, I suppose LiLo has similar capabilities.) Those are the lines, I appended to the top of my menu.lst : serial --unit=0 --speed=38400 --word=8 --parity=no --stop=1 terminal --timeout=3 serial console The serial command initiates the serial terminal option, --unit=0 defines our first serial connector, I my case, it's the only one I have on my machine. I used the standard Linux-Console speed, as well as the "8N1" connection strategy. terminal defines the terminal priorities, first terminal (serial) is the standard one, the last one is the secondary terminal (console). --timeout=3 enables a delay on both consoles, with a prompt for a keystroke. Depending on which terminal, the key is pressed, this terminal, will be used. If no key is pressed after the timeout, the standard console (in my case serial) will be used. # Relaying Kernel output on boot The Kernel accepts multiple console options, of which the last one, is the standard console, and the one that will be used in Single User mode. These are my Kernel options: title Fedora Core (2.6.20-1.2316.fc5) root (hd0,0) kernel /vmlinuz-2.6.20-1.2316.fc5 ro root=/dev/VolGroup00/LogVol00 rhgb quiet vga=795 console=tty0 console=ttyS0,38400 initrd /initrd-2.6.20-1.2316.fc5.img console=tty0 is the standard console, located on the machine, i.e. monitor and keyboard.

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