"Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid." – Albert Einstein

Linux cmd Page 2

11. alsactl

alsactl [options] [store|restore] card

Controls advanced configuration settings for sound cards using the ALSA (Advanced Linux Sound Architecture) system. Settings are written to configuration files using the store function and loaded from those files with the restore function.



Debug mode: increased information output to the console.

-f file, –f=file

Specify the use of file instead of /etc/asound.state as a configuration file.


Force the restoration of settings.


Display help message and quit.


Display version information and quit.

12. amidi

amidi [options]

Read and write raw MIDI files (.syx format, without timing information) to ALSA ports. For standard MIDI (.mid) files, use aplaymidi and arecordmidi.



Record and send active-sensing (FEh) bytes in MIDI commands. By default, these bytes are ignored.


Output all received data directly to the screen.


Display help information and quit.


List all hardware MIDI ports.


List all RawMIDI definitions. Useful for debugging configuration files.


Use the specified port. This overrides the port set in the configuration file. If neither this flag nor the configuration file sets a port, the default is port 0 on device 0, which may or may not exist.


Write data from the port specified with the -p or –port flag to the file named here. This will be a raw file, and should end in .syx. Unless you use the -a option, it will not contain any Active Sensing (FEh) bytes.


Send the file to the port specified with the -p or –port flag. Use raw (.syx) MIDI files only.


Send a string of hexadecimal numbers to the port specified with the -p or –port flag.


Stop listening after n seconds of receiving no data.


Display version information and quit.

13. amixer

amixer [-ccard] [command]

Command-line ALSA mixer. For an ncurses interface, use alsamixer. amixer displays or changes the current mixer settings for the current sound card and sound device. To display all mixer settings, use with no flags or commands.



Displays a complete list of card controls. These controls can be set with the cset command, in contrast to simple mixer controls, which use set or sset.


List card controls and their contents.

cget [control]

Display the contents of the specified card control.

cset [control] [parameter]

Set the card control to the value specified in the parameter. Card controls may be identified by iface, name, index, device, subdevice, or numid. The parameter will normally be a number or percentage value. For example, the command amixer -c 1 cset numid=16 50% will set the 16th element of the first sound card to 50%.

get,sget [control]

Display the current values for the specified control.


Display help message and quit.


Displays information about the card specified with the -c flag.


Display a list of simple mixer controls. Simple mixer controls can be set with the set or sset commands, in contrast to card controls, which use the cset command.

set,sset [control] [parameter]

Set one of the controls listed by scontrols. You can specify the volume with a percentage from 0% to 100%, or a specific hardware value. By appending + or – to the number, you will increase or decrease the volume by that amount. To set recording and muting values, use the parameters cap (meaning capture, or record), nocap,mute,unmute, or toggle. To specify individual channels, use the parameters front, rear, center, or woofer. For example, the command amixer -c 1 sset Line,0 100% unmute will set Line 0 on the first sound card to 100% and unmute it.


-c n

The number of the card to adjust.

-D devicename

Specify the name of the device. By default, the name is default.


Display help information and quit.


Quiet mode: do not show the results of changes made.

14. anacron

anacron [options] [job]

System administration command. Normally started in a system startup file. Execute commands periodically. By default, anacron reads a list of jobs from a configuration file, /etc/anacrontab. The file consists of shell variables to use when running commands, followed by a list of tasks to run. Each task specifies how often in days it should be run, a delay in minutes to wait before running the task, a unique job identifier used to store a timestamp, and the shell command to execute. Timestamps for the last run of each task are stored in the /var/spool/anacron file. For each task, anacron compares the stored timestamp against the current time. If the command has not been executed within the specified frequency, the command is run. Upon completion, anacron records the new date in the timestamp file. Limit anacron to a specified task by providing the task’s unique job identifier on the command line.

The anacron command is often used to support the cron daemon on systems that do not run continuously.



Run in foreground rather than as a background process. Send messages to standard error.


Run tasks ignoring timestamps.


Print help message, then exit.


Run tasks now, ignoring delay specifications.


Suppress messages to standard error when using the -d option.


Execute tasks serially. Do not start new task until previous task is completed.

-t file

Read tasks from file instead of from /etc/anacrontab.


Update timestamps for tasks, but don’t run them.


Print version number, then exit.

15. aplay

aplay [options] [file]

Play sound files using the ALSA sound system. The related arecord records sound files.



Print help message, then exit.


Print version and quit.


List available sound cards and digital audio devices.


List all PCM (pulse-coded modulation, or digital audio) devices that have been defined. PCMs may be defined in the .asoundrc file.


Select a PCM device by name.


Do not display messages.


Name the file type used. Files may be voc, wav, raw, or au.


Use n channels: 1 for mono, 2 for stereo.


Specify the sample format. The sample formats available will depend on hardware. For CD and DAT output, use the cd and dat shortcuts, which set the sample rate, format, and channel numbers all at once.


Set the sample rate in Hertz.


Set an interrupt for n seconds after playback begins.


16. aplaymidi

aplaymidi [options] [file]

Play MIDI files using the ALSA sound system; output is to ALSA sequencer ports.



Delay n seconds at the end of a file to allow for reverberation of the final notes.


Print help message, then exit.


Print version and quit.


List output ports available.


Specify the port to which the MIDI file will be sent. If no port is specified, the file will be sent to port 0.

17. apm

apm [options]

Display current Advanced Power Management hardware information, such as battery life, or send the system into standby or suspend-to-disk mode. Used on older systems, and replaced by acpi and related commands.

-V, –version

Display version information and quit.


Verbose mode. Display information about the APM BIOS and Linux APM driver.

-m, –minutes

Display estimated minutes of battery life remaining. Default format is in hours and minutes.

-s, –suspend

Suspend system to disk. Suspending the system to disk is equivalent to turning it off, but boot time will be faster and the system will resume exactly where it was before suspend.

-S, –standby

Set system to standby. This will normally turn off the monitor and spin down the disk drives, reducing energy consumption by approximately 50 percent. Recovery from this mode is more rapid than from a full suspend to disk, but the system is still running.


When the system is using AC power, ignore suspend or standby requests generated by the system.


Do not ignore any suspend or standby events. This overrides a previously issued -i flag.

18. apmd

apmd [options]

System administration command. apmd handles events reported by the Advanced Power Management BIOS driver. The driver reports on battery level and requests to enter sleep or suspend mode. apmd will log any reports it gets via syslogd and take steps to make sure that basic sleep and suspend requests are handled gracefully. You can fine-tune the behavior of apmd by editing the apmd_proxy script, which apmd runs when it receives an event. Note that the APM hardware standard is gradually being replaced by the ACPI (Advanced Configuration and Power Interface) standard, and apmd by acpid. On SUSE Linux, both APM and ACPI hardware are handled by powersave and powersaved.


-c n, –check n

Set the number of seconds to wait for an event before rechecking the power level. Default is to wait indefinitely. Setting this causes the battery levels to be checked more frequently.

-p n, –percentage n

Log information whenever the power changes by n percent. The default is 5. Values greater than 100 will disable logging of power changes.

-P command, –apmd_proxy command

Specify the apmd_proxy command to run when APM driver events are reported. This is generally a shell script. The command will be invoked with parameters indicating what kind of event was received. The parameters are listed in the next section.

-v, –verbose

Verbose mode; all events are logged.

-V, –version

Print version and exit.

-w n, –warn n

Log a warning at ALERT level when the battery charge drops below n percent. The default is 10. Negative values disable low-battery-level warnings.

-W, –wall

Use wall to alert all users of a low battery status.

-q, –quiet

Disable low-battery-level warnings.

-?, –help

Print help summary and exit.


The apmd proxy script is invoked with the following parameters:


Invoked when the daemon starts.


Invoked when the daemon stops.

suspend [ system | user ]

Invoked when the daemon receives a suspend request. The second parameter indicates whether the request was made by the system or by the user. Suspend, also known as “hibernate,” effectively powers the system down but has a quicker recovery than a normal boot process.

standby [ system | user ]

Invoked when the daemon receives a standby request. The second parameter indicates whether the request was made by the system or by the user. Standby mode powers off the monitor and disks, but the system continues to run and use power.

resume [ suspend | standby | critical ]

Invoked when the system resumes normal operation. The second parameter indicates the mode the system was in before resuming. critical suspends indicate an emergency shutdown. After a critical suspend, the system may be unstable, and you can use the resume command to help you recover from the suspension.

change power

Invoked when system power is changed from AC to battery or from battery to AC.

change battery

Invoked when the APM BIOS driver reports that the battery is low.

change capability

Invoked when the APM BIOS driver reports that some hardware that affects its capability has been added or removed.

19. apropos

apropos string …

Search the short manual page descriptions in the whatis database for occurrences of each string and display the result on the standard output. Like whatis, except that it searches for strings instead of words. Equivalent to man -k.

20. apt


The Advanced Package Tool, the Debian package management system. A freely available packaging system for software distribution and installation. For detailed information on apt and its commands, see Chapter 5.


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