Linux Commands Examples

A great documentation place for Linux commands


ASCII, decimal, hexadecimal, octal dump

see also : gdb - od


hexdump [-bcCdovx] [-e format_string] [-f format_file] [-n length] [-s skip] file ...
[-bcdovx] [-e format_string] [-f format_file] [-n length] [-s skip] file ...

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Display the input in perusal format:

"%06.6_ao " 12/1 "%3_u "
"\t\t" "%_p "

Implement the -x option:

"%07.7_ax " 8/2 "%04x " "\n"

Some examples for the -e option:

# hex bytes
% echo hello | hexdump -v -e ’/1 "%02X "’ ; echo
68 65 6C 6C 6F 0A

# same, with ASCII section
% echo hello | hexdump -e ’8/1 "%02X ""\t"" "’ -e ’8/1 "%c""\n"’
68 65 6C 6C 6F 0A hello

# hex with preceding ’x’
% echo hello | hexdump -v -e ’"x" 1/1 "%02X" " "’ ; echo
x68 x65 x6C x6C x6F x0A

# one hex byte per line
% echo hello | hexdump -v -e ’/1 "%02X\n"’

# a table of byte#, hex, decimal, octal, ASCII
% echo hello | hexdump -v -e ’/1 "%_ad# "’ -e ’/1 "%02X hex"’ -e ’/1 " = %03i dec"’ -e ’/1 " = %03o oct"’ -e ’/1 " = _%c\_\n"’
0# 68 hex = 104 dec = 150 oct = _h_
1# 65 hex = 101 dec = 145 oct = _e_
2# 6C hex = 108 dec = 154 oct = _l_
3# 6C hex = 108 dec = 154 oct = _l_
4# 6F hex = 111 dec = 157 oct = _o_
5# 0A hex = 010 dec = 012 oct = _

# byte# & ASCII with control chars
% echo hello | hexdump -v -e ’/1 "%_ad# "’ -e ’/1 " _%_u\_\n"’
0# _h_
1# _e_
2# _l_
3# _l_
4# _o_
5# _lf_

phd $0 hd hd

What should I upgrade on my Linux media PC to stop 1080p video issues?

Video card. Get an nVidia card with the highest VDPAU set.
Check this table to find a card which fits your need. (You don't have to spend too much, even the newer, low-performance cards are perfect to play back the highest definition. Like GT240 at the moment.)

You will play your movies with vdpau this way.

(You may need this PPA later, when you install the card, in order to install the necessary software support. PPAs are for Ubuntu, they stand for a personal package archive. However, I used many Linux distributions, and every distro ships with vdpau support nowadays.)


720p videos get choppy and freeze constantly when played on my netbook

vlc does not use gpu acceleration as a default, and even when activated it's experimental as of now. Check for prerequisites and codecs.

Assuming it's not activated your cpu (netbook = atom?) most likely has difficulties to keep pace.

Have you tried mplayer?


Do Intel HD 3000 Graphics run out of the box on Linux?

Ubuntu 11.04 beta seems to support the graphics drivers out of the box, as per this discussion.

As an opinion for game, here's a quote from the same discussion

I am getting stutter in some games, which are mainly in wine, or java (minecraft).


Which camera i can use in my laptop to have more better quality then Iphone tiny camera?

  • Note: This is a shopping question BUT this is NOT a shopping answer per se. It is a "do your homework as well as you can before asking and you will get better results, and here is how to do it and why you want to" type answer :-). As such it is applicable to both shopping and technical questions and may (or may not) have a place here.

The technically competent may enjoy the last two references.

This is very very much a shopping type question. It doesn't need to be. This is probably not the right place for the question regardless, but you would help yourself by learning how to ask it better. (Questions that relate to "shopping" re electronic design decisions have their place here, I think (fwiw)).

In this case (and in most cases) if you do your homework BEFORE asking questions like this you will be better able to judge if the answers are good ones.

Note that high megapixels and high photo quality are not identical - BUT you asked in terms of megapixels. If you are not 100% sure that a feature such as megapixels is directly related to another attribute such as quality then you should be exceptionally careful about talking about one when you mean the other. eg the Sony A850 & A950 DSLR cameras have 24+ MP sensors and produce the most detailed studio shots available from a 35mm DSLR camera. But if you take photos on low light or focus on (pun almost intended) sports photography then a 12 MP Nikon D700 or the even better D800s will produce vastly superior "quality". So, here, 12 MP >> 24 MP for "quality".

The "clear" answer to your question is:

  • "The camera that you can find advertised that you consider is much better then the one on an iphone because you understand the differences - and which has 1080p video, and AVCHD and/or 50p or 60p rating, and which has the highest possible megapixel rating for still shots (probably in the 12-20 MP range, but maybe higher)." Whew!

While this answer has replaced your general terms with "buzz words" / jargon they are the sort of terms that you are going to underatnd at least a little in order to make a good choice. If you ask general questions, as you have done, without doing any homework re the terminology used and the facilities available, you run the severe risk of accepting a recommendation that is uninformed and that does not meet your needs as well as they could have been met.

  • eg "What is the difference between (720i), 720p, 1080i, 1080p, what do these terms mean, and why should you care?. And do you care?"

A little searching will produce comments like:

  • The AVCHD video format specification has been updated to include 1080 60p and 50p video. The AVCHD 2.0 standard has been approved by Sony and Panasonic - the co-promoters of the format. The move also includes additional support for high definition 3D movies in the format. Up until now, both companies have made high-end camcorders that incorporated out-of-specification 60p video in what was otherwise an AVCHD arrangement.

Which will help guide further searching as you begin to better understand the subject.

Research 1080p (and the others mentioned above - you want 1080p) Research 50p, 60p, AVCHD - what you want is less certain. But when you have finished you will know what you want and why.

  • Google ( is your great friend.

  • is a pretty good friend as well - sometimes better than Google.

So, all that said, the following may give you a good start on your quest:

  • 720p - 720 lines of video - better quality than "TV"

  • 1080i / 1080p - 1080 lines of video - better quality than 720. You want 1080p - see below.

  • xxxi = interlaced - picture is delivered in two consecutive "frames" each having half the information. Standard TV does this. Lower cost to implement and to transmit. Has "issues" Avoid.

  • xxxp = non interlaced. All picture information in one "frame". Better quality. Buy it

  • 50p / 60p = 50 or 60 frames per second. Faster than TV (50i or 60i) or "standard " video 30x (or film at 24fps but a whole new (vast) subject). 50p for 50 Hz mains areas (eg UK). 60p for 60 Hz mains areas (eg USA). Much better potenr=tial motion handling and slo-mo and ... than 30p etc.

  • AVCHD Wikipedia - AVCHD.


Steven says this looks better - Search the web for 1080p 50p 60p:


1080p 50p samples. Wow. Note that the 1080 affects the resolution and the xxxxp and 50p affect the motion handling.

50p and slow motion playing

Brain hurting time :-) 24PA, 24F, 24P, 25F, 25P, 30F, 30P explained

Deep magic. Only for techo-freaks


Video playback shows fault lines where it looks like parts of two frames are being spliced together (edit: called "tearing")

This doesn't look like an issue with any specific frame. Rather, it's probably your video card being too overwhelmed to display the video without lagging. Do you notice more tearing with higher-resolution videos? More pixels means more work for your hardware. High framerates can cause also more work, as it has less time to process all those tiny pixels in a given frame.

You should try experimenting with different Video Output drivers. IDK about VLC, but Mplayer does best with XV. If you and use XV with so-called "adaptors", that may help improve your performance even further (eg, -vo xv:adaptor=0). If you still experience tearing, you can try using software scaling to reduce the resolution (-vf-add scale=720), if you have a fast CPU.

If all of the above fails, your GPU probably just plain isn't fast enough for HD video. You could try buying a newer, faster model. Or, you could probably use a video converter program, such as FFMpeg, to convert the video at a lower resolution. If you don't like command-lines, you could also use XMedia-Recode (a Windows-based GUI), as it works quite well with WINE. The homepage is in German, but you can download it from Video Help, if you feel more comfortable getting it from an English site. Either way, XMR will work in English.


Is there ultra HD support in Linux?

As Linux uses X11 to do graphical rendering, this question is really about whether X11 supports it.

The answer is yes, X11 supports arbitrary sizes. One example with 4K HD is here.


The hexdump utility is a filter which displays the specified files, or the standard input, if no files are specified, in a user specified format.

The options are as follows:


One-byte octal display. Display the input offset in hexadecimal, followed by sixteen space-separated, three column, zero-filled, bytes of input data, in octal, per line.


One-byte character display. Display the input offset in hexadecimal, followed by sixteen space-separated, three column, space-filled, characters of input data per line.


Canonical hex+ASCII display. Display the input offset in hexadecimal, followed by sixteen space-separated, two column, hexadecimal bytes, followed by the same sixteen bytes in %_p format enclosed in ’’|’’ characters.

Calling the command hd implies this option.


Two-byte decimal display. Display the input offset in hexadecimal, followed by eight space-separated, five column, zero-filled, two-byte units of input data, in unsigned decimal, per line.

-e format_string

Specify a format string to be used for displaying data.

-f format_file

Specify a file that contains one or more newline separated format strings. Empty lines and lines whose first non-blank character is a hash mark (#) are ignored.

-n length

Interpret only length bytes of input.


Two-byte octal display. Display the input offset in hexadecimal, followed by eight space-separated, six column, zero-filled, two byte quantities of input data, in octal, per line.

-s offset

Skip offset bytes from the beginning of the input. By default, offset is interpreted as a decimal number. With a leading 0x or 0X, offset is interpreted as a hexadecimal number, otherwise, with a leading 0, offset is interpreted as an octal number. Appending the character b, k, or m to offset causes it to be interpreted as a multiple of 512, 1024, or 1048576, respectively.


Cause hexdump to display all input data. Without the -v option, any number of groups of output lines, which would be identical to the immediately preceding group of output lines (except for the input offsets), are replaced with a line comprised of a single asterisk.


Two-byte hexadecimal display. Display the input offset in hexadecimal, followed by eight, space separated, four column, zero-filled, two-byte quantities of input data, in hexadecimal, per line.

For each input file, hexdump sequentially copies the input to standard output, transforming the data according to the format strings specified by the -e and -f options, in the order that they were specified.

A format string contains any number of format units, separated by whitespace. A format unit contains up to three items: an iteration count, a byte count, and a format.

The iteration count is an optional positive integer, which defaults to one. Each format is applied iteration count times.

The byte count is an optional positive integer. If specified it defines the number of bytes to be interpreted by each iteration of the format.

If an iteration count and/or a byte count is specified, a single slash must be placed after the iteration count and/or before the byte count to disambiguate them. Any whitespace before or after the slash is ignored.

The format is required and must be surrounded by double quote (" ") marks. It is interpreted as a fprintf-style format string (see fprintf(3)), with the following exceptions:

An asterisk (*) may not be used as a field width or precision.

A byte count or field precision is required for each ’’s’’ conversion character (unlike the fprintf(3) default which prints the entire string if the precision is unspecified).

The conversion characters ’’%’’, ’’h’’, ’’l’’, ’’n’’, ’’p’’ and ’’q’’ are not supported.

The single character escape sequences described in the C standard are supported:

NUL \0
<alert character> \a
<backspace> \b
<form-feed> \f
<newline> \n
<carriage return> \r
<tab> \t
<vertical tab> \v

The hexdump utility also supports the following additional conversion strings:


Display the input offset, cumulative across input files, of the next byte to be displayed. The appended characters d, o, and x specify the display base as decimal, octal or hexadecimal respectively.


Identical to the _a conversion string except that it is only performed once, when all of the input data has been processed.


Output characters in the default character set. Nonprinting characters are displayed in three character, zero-padded octal, except for those representable by standard escape notation (see above), which are displayed as two character strings.


Output characters in the default character set. Nonprinting characters are displayed as a single ’’.’’.


Output US ASCII characters, with the exception that control characters are displayed using the following, lower-case, names. Characters greater than 0xff, hexadecimal, are displayed as hexadecimal strings.

000 NUL 001 SOH 002 STX 003 ETX 004 EOT 005 ENQ
006 ACK 007 BEL 008 BS 009 HT 00A LF 00B VT
00C FF 00D CR 00E SO 00F SI 010 DLE 011 DC1
012 DC2 013 DC3 014 DC4 015 NAK 016 SYN 017 ETB
018 CAN 019 EM 01A SUB 01B ESC 01C FS 01D GS
01E RS 01F US 07F DEL

The default and supported byte counts for the conversion characters are as follows:

%_c, %_p, %_u, %c

One byte counts only.

%d, %i, %o, %u, %X, %x

Four byte default, one, two and four byte counts supported.

%E, %e, %f, %G, %g

Eight byte default, four and twelve byte counts supported.

The amount of data interpreted by each format string is the sum of the data required by each format unit, which is the iteration count times the byte count, or the iteration count times the number of bytes required by the format if the byte count is not specified.

The input is manipulated in ’’blocks’’, where a block is defined as the largest amount of data specified by any format string. Format strings interpreting less than an input block’s worth of data, whose last format unit both interprets some number of bytes and does not have a specified iteration count, have the iteration count incremented until the entire input block has been processed or there is not enough data remaining in the block to satisfy the format string.

If, either as a result of user specification or hexdump modifying the iteration count as described above, an iteration count is greater than one, no trailing whitespace characters are output during the last iteration.

It is an error to specify a byte count as well as multiple conversion characters or strings unless all but one of the conversion characters or strings is _a or _A.

If, as a result of the specification of the -n option or end-of-file being reached, input data only partially satisfies a format string, the input block is zero-padded sufficiently to display all available data (i.e., any format units overlapping the end of data will display some number of the zero bytes).

Further output by such format strings is replaced by an equivalent number of spaces. An equivalent number of spaces is defined as the number of spaces output by an s conversion character with the same field width and precision as the original conversion character or conversion string but with any ’’+’’, ’’ ’’, ’’#’’ conversion flag characters removed, and referencing a NULL string.

If no format strings are specified, the default display is equivalent to specifying the -x option.

exit status

The hexdump and hd utilities exit 0 on success, and >0 if an error occurs.

see also

gdb , od

BSD February 18, 2010 BSD

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