linux display screens free sample

Brief: In this guide, we will discuss some useful examples of the screen command. By the end of this guide, users will be able to work with multiple shell sessions using a single Linux terminal window.

As Linux users, we often need to work on long-running tasks, such as – downloading or copying large files, executing time-consuming database queries, and so on. Sometimes these important tasks get terminated abruptly due to a session timeout.

In this guide, we will discuss how to install, configure, and use the screen command on a Linux system. Throughout this guide, we will understand the usage and benefits of the screen command using practical examples.

On my Ubuntu Server Edition, the screen command has been installed by default. But, Linux Mint does not have a screen installed by default, so I need to install it first using the

Sometimes it is important to record what you have done while you are in the console. Let’s say you are a Linux Administrator who manages a lot of Linux servers.

With this screen logging, you don’t need to write down every single command that you have done. To activate the screen logging function, just press “Ctrl-A” and “H“. (Please be careful, we use a capital ‘H’ letters. Using non-capital ‘h’, will only create a screenshot of the screen in another file named hardcopy).

A Password will be asked to you twice. The first password is your Linux password, and the second password is the password that you put in your .screenrc file.

While using LINUX there might come a situation when you are willing to install a new application (big in size) and you wish to know for the amount of free memory available on your system. In LINUX, there exists a command line utility for this and that is freecommand which displays the total amount of free space available along with the amount of memory used and swap memory in the system, and also the buffers used by the kernel.

As free displays the details of the memory related to your system , its syntax doesn’t need any arguments to be passed but only options which you can use according to your wish.

When no option is used then free command produces the columnar output as shown above where column:total displays the total installed memory (MemTotal and SwapTotal i.e present in /proc/meminfo).

-h, – -human : It shows all output columns automatically scaled to shortest three digit unit and display the units also of print out. The units used are B(bytes), K(kilos), M(megas), G(gigas), and T(teras).

-s, – -seconds : This option allows you to display the output continuously after s seconds delay. In actual, the usleepsystem call is used for microsecond resolution delay times.

6. Using -s and -o: This option allows you to display the output of free command after a set time gap given by the user. This option requires a numeric value to be passed with it that is treated as the number of seconds after which the output will be displayed.//using free with -s

Now, with -s you can only specify the time gap but not the number of times you want the output to be displayed. For this, -cis used along with -s specifying the number of times the output will be displayed.

First, you’ll want to see if this software is already included with your Linux distribution. Many modern distributions include it, but it’s usually easy to install otherwise.

It’s important to note that these shortcuts are case-sensitive. Like most things on linux, they can also be customized. This can be achieved by editing the .screenrc file which can usually be found in /etc/screenrc.

In the table, you can see the option to rename windows. This is different than the naming of screens you performed earlier with screen -S [name]. You will notice the window name in the bottom left corner. You can get a list of windows with their corresponding names and ID’s by entering [ ctrl + a ] + ["].

will display a list of the available screen commands and their bindings. Each keystroke is discussed in the section "DEFAULT KEY BINDINGS". The manual

will cause the interrupt key (usually C-c) to interrupt the display immediately when flow-control is on. See the "defflow" .screenrc command for details.

(other)Toggle to the window displayed previously. Note that this binding defaults to the command character typed twice, unless overridden. For instance, if you use

Execute a command at other displays or windows as if it had been entered there. "At" changes the context (the "current window" or "current display" setting)

identifier in front of the "#", "*" or "%"-character selects all users, displays or windows because a prefix-match is performed. Note that on the affected

display(s) a short message will describe what happened. Permission is checked for initiator of the "at" command, not for the owners of the affected display(s).

"other") may be called again. In shared windows the command will be repeated for each attached display. Beware, when issuing toggle commands like "login"! Some

commands (e.g. "process") require that a display is associated with the target windows. These commands may not work correctly under "at" looping over windows.

Change background-color-erase setting. If "bce" is set to on, all characters cleared by an erase/insert/scroll/clear operation will be displayed in the

bind \033 screen -ln -t root -h 1000 9 suwould bind the space key to the command that displays a list of windows (so that the command usually invoked by "C-a C-w" would also be available as "C-a

behaves identical to "defbreaktype". This will be changed in the future. Calling "breaktype" with no parameter displays the break method for the current

This command controls the display of the window captions. Normally a caption is only used if more than one window is shown on the display (split screen

!/bin/shCreates another shell in the same window, while the original shell is still running. Output of both shells is displayed and user input is sent to the new

line to display messages. If the flag is set to "off", these messages are overlaid in reverse video mode at the display line. The default setting is "on".

Set the display height to a specified number of lines. When no argument is given it toggles between 24 and 42 lines display. You can also specify a width if

their current bindings. Subsequent pages will display the custom commands, one command per key. Press space when you"re done reading each page, or return to

exit early. All other characters are ignored. If the "-c" option is given, display all bound commands for the specified command class. See also "DEFAULT KEY

-(-)flow flow control disabled. Agrees with automatic control.The current line wrap setting ("+wrap" indicates enabled, "-wrap" not) is also shown. The flags "ins", "org", "app", "log", "mon" or "nored" are displayed

Redisplay the last contents of the message/status line. Useful if you"re typing when a message appears, because the message goes away when you press a key

Lock this display. Call a screenlock program (/local/bin/lck or /usr/bin/lock or a builtin if no other is available). Screen does not accept any command

notification message in the status line at the first sign of output and the window will also be marked with an "@" in the window-status display. Monitoring is

Tell screen how to deal with user interfaces (displays) that cease to accept output. This can happen if a user presses ^S or a TCP/modem connection gets cut

"blocked" and stop sending characters to it. If at some time it restarts to accept characters, screen will unblock the display and redisplay the updated window

argument, the displays paste buffer is the destination. Note, that "paste" uses a wide variety of resources: Whenever a second argument is specified no current

window is needed. When the source specification only contains registers (not the paste buffer) then there need not be a current display (terminal attached), as

this session is displayed. Caution: The $STY environment variables still reflects the old name. This may result in confusion. The default is constructed from

Split the current region into two new ones. All regions on the display are resized to make room for the new region. The blank window is displayed on the new

Uses the message line to display the time of day, the host name, and the load averages over 1, 5, and 15 minutes (if this is available on your system). For

parameter toggles the setting. If a second parameter is given, the display"s encoding is also changed (this should rather be done with screen"s "-U" option).

visual bell, a "vbell-message" is displayed in the status line when the bell character (^G) is received. Visual bell support of a terminal is defined by the

Display all windows in a table for visual window selection. The desired window can be selected via the standard movement keys (see the "copy" command) and

Uses the message line to display a list of all the windows. Each window is listed by number with the name of process that has been started in the window (or

use this for displaying its messages, otherwise a line of the current screen will be temporarily overwritten and output will be momentarily interrupted. The

pad the string to the display"s width (like TeX"s hfill). If a number is specified, pad to the percentage of the window"s width. A "0" qualifier tells

clear all attributes, write in default color on yellow background.%-Lw%{= BW}%50>%n%f* %t%{-}%+Lw%

If you"re running with flow-control enabled and find that pressing the interrupt key (usually C-c) does not interrupt the display until another 6-8 lines

switch screens and return, or update the screen with "C-a l" you would see the version of the output you would have gotten without "interrupt" being on. Also,

Normally the name displayed is the actual command name of the program created in the window. However, it is sometimes useful to distinguish various programs of

part of the prompt"s length. If these invisible characters aren"t a multiple of 8 then backspacing over a tab will result in an incorrect display. One way to

hardstatus line. If the display has no hardstatus the line will be displayed as a standard screen message. The hardstatus line can be changed with the

What happens when you cat out a file that’s larger than your console can display and so some content scrolls past? To scroll back in the buffer, hit Ctrl+A and then Esc. You’ll now be able to use the cursor keys to move around the screen and go back in the buffer.

free is a popular command used by system administrators on Unix/Linux platforms. It"s a powerful tool that gives insight into the memory usage in human-readable format.

The man page for this command states that free displays the total amount of free and used memory on the system, including physical and swap space, as well as the buffers and caches used by the kernel. The information is gathered by parsing /proc/meminfo.

Like any other command, free has gone through revisions over time to make its output meaningful and accurate for decision making. In Red Hat Enterprise Linux (RHEL) 6, the output is somewhat different from that of RHEL 7 and 8. However, in all these versions, there are key parameters that do not change.

free -b, -k, -m, -g: Display the amount of memory in bytes, kilobytes, megabytes, gigabytes respectively. You can also use free -h to show output in human-readable output. Please run free --help for more information on the options.

The various columns, displayed by the various releases above, seek to identify the Total, used, free, shared memory. It also seeks to display the memory held in cache and buffers as well.

In figure 1 above, the total is 94 GB, used is 44 GB, and free is 49 GB. This system is quite busy, but the used RAM seems high. This shouldn"t cause much concern, but the admin needs to look at the -/+ buffers/cache column. The -/+ buffers/cache displays used memory as 42 GB and free memory as 52 GB. This means that the actual quantity of used RAM is 42 GB and not 44 GB. The value 44 GB includes the cache as well. A mere look at the used value without considering the cache affects your interpretation of the system"s performance.

On Unix-like operating systems, the free command displays the total amount of free and used physical and swap memory, and the buffers used by the kernel.

Continuously display the result delay seconds apart. You may actually specify any floating point number for delay. The usleep system call is used for microsecond resolution delay times.

When using the free command, the two important lines are the -/+ buffers/cache line and Swap line. If you want to get a good idea on how much free memory is available, the free section in the buffers/cache is what you should be reading. Linux keeps the contents of memory in the buffers to help having to access the same data over-and-over from the slower disk drive. If your buffers/cache free memory is low or your swap free is low, a memory upgrade is necessary.

Linux compatibility with digital signage software solutions have long been sought after. Linux solutions, like Ubuntu, are free and offer cost savings for businesses. Schools have used Ubuntu and digital signage together to create STEM programming, office signage, CAP alerts, menu boards, and more!

Ubuntu has typically used Firefox, which is a great solution. The browser used to show presentations on the Rise Vision"s easy to use platform using a Linux version of Google Chrome called Chromium. It’s another open source software that is free to use.

Ubuntu is a great option for digital signage. You can make things interactive or static. The system will remain stable no matter what the display is showing.

There have been a couple common items to configure with your Linux Ubuntu display. An additional issue that may arise is having the mouse cursor appear over your presentation. You can solve this issue with the information in this post.

One great feature of the service that you can configure at this point is to setup remote support so you can work on multiple displays from a central location.

The biggest appeal of Linux Ubuntu is that it’s part of the free software movement. Instead of paying high fees for your digital signage operating system you can use Ubuntu to get the same results. Some would even consider it to be the better option.

Ubuntu can handle the large work a big presentation often requires. It’s a great solution for running many different displays because you can scale the software for no cost and the system will maintain stability.

Such tools are available for all popular platforms, including Windows, Mac and Linux. In this roundup, we take a look at five popular free and open-source screen recording applications for Linux: Byzanz, Kazam, RecordMyDesktop, ScreenStudio and SimpleScreenRecorder.

When run through the command line, Kazam also offers a "God Mode" feature that lets you capture (in still screenshots) both the currently active window and the whole desktop in one go.

For example, those looking to live-stream their recording can choose between Kazam, ScreenStudio and SimpleScreenRecorder, but if webcam support is also a requirement, then the former two are the better choices. Similarly, if you’re looking for an app that can record for a predefined period of time or just until a command has finished executing, then Byzanz is your best bet.

And you are live! Your player will automatically start displaying your playlist. Watch your own Digital signage channel on your display(s). Try Opensignage now and experience how easy and user-friendly Digital Signage can be!

You can do verification measurements to assess the display chain"s (display profile - video card and the calibration curves in its gamma table - monitor) fit to the measured data, or to find out about the soft proofing capabilities of the display chain. You can also do a profile or device link (3D LUT) self check without having to take any further measurements by holding the “alt” key on your keyboard.

To check the fit to the measurement data, you have to select a CGATS testchart file containing device values (RGB). The measured values are then compared to the values obtained by feeding the device RGB numbers through the display profile (measured vs expected values). The default verification chart contains 26 patches and can be used, for example, to check if a display needs to be re-profiled. If a RGB testchart with gray patches (R=G=B) is measured, like the default and extended verification charts, you also have the option to evaluate the graybalance through the calibration only, by placing a check in the corresponding box on the report.

To perform a check on the soft proofing capabilities, you have to provide a CGATS reference file containing XYZ or L*a*b* data, or a combination of simulation profile and testchart file, which will be fed through the display profile to lookup corresponding device (RGB) values, and then be sent to the display and measured. Afterwards, the measured values are compared to the original XYZ or L*a*b* values, which can give a hint how suitable (or unsuitable) the display is for softproofing to the colorspace indicated by the reference.

The profile that is to be evaluated can be chosen freely. You can select it in DisplayCAL"s main window under “settings”. The report files generated after the verification measurements are plain HTML with some embedded JavaScript, and are fully self-contained. They also contain the reference and measurement data, which consists of device RGB numbers, original measured XYZ values, and D50-adapted L*a*b* values computed from the XYZ numbers, and which can be examined as plain text directly from the report at the click of a button.

There are two sets of default verification charts in different sizes, one for general use and one for Rec. 709 video. The “small” and “extended” versions can be used for a quick to moderate check to see if a display should be re-profiled, or if the used profile/3D LUT is any good to begin with. The “large” and “xl” versions can be used for a more thorough check. Also, you can create your own customized verification charts with the testchart editor.

Checking how well a display can simulate another colorspace (evaluating softproofing capabilities, 3D LUTs, DeviceLink profiles, or native display performance)

Whitepoint simulation. If you are using a reference file that contains device white (100% RGB or 0% CMYK), or if you use a combination of testchart and simulation profile, you can choose if you want whitepoint simulation of the reference or simulation profile, and if so, if you want the whitepoint simulated relative to the display profile whitepoint. To explain the latter option: Let"s assume a reference has a whitepoint that is slightly blueish (compared to D50), and a display profile has a whitepoint that is more blueish (compared to D50). If you do not choose to simulate the reference white relative to the display profile whitepoint, and the display profile"s gamut is large and accurate enough to accomodate the reference white, then that is exactly what you will get. Depending on the adaptation state of your eyes though, it may be reasonable to assume that you are to a large extent adapted to the display profile whitepoint (assuming it is valid for the device), and the simulated whitepoint will look a little yellowish compared to the display profile whitepoint. In this case, choosing to simulate the whitepoint relative to that of the display profile may give you a better visual match e.g. in a softproofing scenario where you compare to a hardcopy proof under a certain illuminant, that is close to but not quite D50, and the display whitepoint has been matched to that illuminant. It will “add” the simulated whitepoint “on top” of the display profile whitepoint, so in our example the simulated whitepoint will be even more blueish than that of the display profile alone.

Using the simulation profile as display profile will override the profile set under “Settings”. Whitepoint simulation does not apply here because color management will not be used and the display device is expected to be in the state described by the simulation profile. This may be accomplished in several ways, for example the display may be calibrated internally or externally, by a 3D LUT or device link profile. If this setting is enabled, a few other options will be available:

Enable 3D LUT (if using the madVR display device/madTPG under Windows, or a Prisma video processor). This allows you to check how well the 3D LUT transforms the simulation colorspace to the display colorspace. Note this setting can not be used together with a DeviceLink profile.

DeviceLink profile. This allows you to check how well the DeviceLink transforms the simulation colorspace to the display colorspace. Note this setting can not be used together with the “Enable 3D LUT” setting.

Tone response curve. If you are evaluating a 3D LUT or DeviceLink profile, choose the same settings here as during 3D LUT/DeviceLink creation (and also make sure the same display profile is set, because it is used to map the blackpoint).

To check a display that does not have an associated profile (e.g. “Untethered”), set the verification tone curve to “Unmodified”. In case you want to verify against a different tone response curve instead, you need to create a synthetic profile for this purpose (“Tools” menu).

This depends on the chart that was measured. The explanation in the first paragraph sums it up pretty well: If you have calibrated and profiled your display, and want to check how well the profile fits a set of measurements (profile accuracy), or if you want to know if your display has drifted and needs to be re-calibrated/re-profiled, you select a chart containing RGB numbers for the verification. Note that directly after profiling, accuracy can be expected to be high if the profile characterizes the display well, which will usually be the case if the display behaviour is not very non-linear, in which case creating a LUT profile instead of a “Curves + matrix” one, or increasing the number of measured patches for LUT profiles, can help.

If you want to know how well your profile can simulate another colorspace (softproofing), select a reference file containing L*a*b* or XYZ values, like one of the Fogra Media Wedge subsets, or a combination of a simulation profile and testchart. Be warned though, only wide-gamut displays will handle a larger offset printing colorspace like FOGRA39 or similar well enough.

Note that both tests are “closed-loop” and will not tell you an “absolute” truth in terms of “color quality” or “color accuracy” as they may not show if your instrument is faulty/measures wrong (a profile created from repeatable wrong measurements will usually still verify well against other wrong measurements from the same instrument if they don"t fluctuate too much) or does not cope with your display well (which is especially true for colorimeters and wide-gamut screens, as such combinations need a correction in hardware or software to obtain accurate results), or if colors on your screen match an actual colored object next to it (like a print). It is perfectly possible to obtain good verification results but the actual visual performance being sub-par. It is always wise to combine such measurements with a test of the actual visual appearance via a “known good” reference, like a print or proof (although it should not be forgotten that those also have tolerances, and illumination also plays a big role when assessing visual results). Keep all that in mind when admiring (or pulling your hair out over) verification results :)

Different softwares use different methods (which are not always disclosed in detail) to compare and evaluate measurements. This section aims to give interested users a better insight how DisplayCAL"s profile verification feature works “under the hood”.

There are currently two slightly different paths depending if a testchart or reference file is used for the verification measurements, as outlined above. In both cases, Argyll"s xicclu utility is run behind the scenes and the values of the testchart or reference file are fed relative colorimetrically (if no whitepoint simualtion is used) or absolute colorimetrically (if whitepoint simulation is used) through the profile that is tested to obtain corresponding L*a*b* (in the case of RGB testcharts) or device RGB numbers (in the case of XYZ or L*a*b* reference files or a combination of simulation profile and testchart). If a combination of simulation profile and testchart is used as reference, the reference L*a*b* values are calculated by feeding the device numbers from the testchart through the simulation profile absolute colorimetrically if whitepoint simulation is enabled (which will be the default if the simulation profile is a printer profile) and relative colorimetrically if whitepoint simulation is disabled (which will be the default if the simulation profile is a display profile, like most RGB working spaces). Then, the original RGB values from the testchart, or the looked up RGB values for a reference are sent to the display through the calibration curves of the profile that is going to be evaluated. A reference white of D50 (ICC default) and complete chromatic adaption of the viewer to the display"s whitepoint is assumed if “simulate whitepoint relative to display profile whitepoint” is used, so the measured XYZ values are adapted to D50 (with the measured whitepoint as source reference white) using the Bradford transform (see Chromatic Adaption on Bruce Lindbloom"s website for the formula and matrix that is used by DisplayCAL) or with the adaption matrix from the profile in the case of profiles with "chad" chromatic adaption tag, and converted to L*a*b*. The L*a*b* values are then compared by the generated dynamic report, with user-selectable critera and ΔE (delta E) formula.

The gray balance “range” uses a combined delta a/delta b absolute deviation (e.g. if max delta a = -0.5 and max delta b = 0.7, the range is 1.2). Because results in the extreme darks can be problematic due to lack of instrument accuracy and other effects like a black point which has a different chromaticity than the whitepoint, the gray balance check in DisplayCAL only takes into account gray patches with a minimum measured luminance of 1% (i.e. if the white luminance = 120 cd/m², then only patches with at least 1.2 cd/m² will be taken into account).

If you enable “Use absolute values” on a report, the chromatic adaptation to D50 is undone (but the refrence white for the XYZ to L*a*b* conversion stays D50). This mode is useful when checking softproofing results using a CMYK simulation profile, and will be automatically enabled if you used whitepoint simulation during verification setup without enabling whitepoint simulation relative to the profile whitepoint (true absolute colorimetric mode). If you enable “Use display profile whitepoint as reference white”, then the reference white used for the XYZ to L*a*b* conversion will be that of the display profile, which is useful when verifying video calibrations where the target is usually some standard color space like Rec. 709 with a D65 equivalent whitepoint.

Oracle Linux provides tools for monitoring and analyzing system resource usage, as well as tracing tools for diagnosing performance issues in multiple processes and related threads.

The mpstat command is used for collecting and displaying performance statistics for all logical CPUs in the system. When a CPU is occupied by a process, it is unavailable for processing other requests. These other processes must wait until the CPU is free.

The top command provides an ongoing look at processor activity in real time. top displays a list of the most CPU-intensive processes or tasks on the system and provides a limited interactive interface for manipulating processes.

The upper section displays general information such as the load averages during the last 1, 5, and 15 minutes, the number of running and sleeping tasks, and overall CPU and memory usage.

The lower section displays a sorted list of processes, usually by CPU usage, along with their process ID numbers (PIDs), and the user who owns the process. In addition, the outputs displays running time and memory that the processes use.