Linux instructions (3)

Linux instructions (3)
Name:/etc/aliases
Permission: System Administrator
Usage: Use newaliases to update the database
Note:
Sendmail uses a file in/etc/aliases for user name conversion. When Sendmail receives a message to XXX, it sends it to another user based on the content in the aliases file. This function can create a user that is only valid in the mail system. For example, mailing list will use this function, in mailinglist, we may create a mailinglist called redlinux@link.ece.uci.edu, but in fact there is no redlinux user. The actual content of the aliases file is to receive all the messages sent to this user.
The mailing list processing program is responsible for delivery.
/Etc/aliases is a text file. Sendmail requires/etc/aliases. DB in binary format. The function of newaliases is to convert/etc/aliases into a database that Sendmail can understand. Example:

# Newaliases
The following command will do the same thing,
# Sendmail-Bi
Related commands:
Mail, mailq, newaliases, Sendmail
"Mail [Return]
Name: Mail
Permission: All Users
Usage: Mail [-iinv] [-s subject] [-c cc-ADDR] [-B bcc-ADDR] user1 [user 2...]
Note:
Mail is not only a command, but also an email program. But there should be very few people who use mail to read emails! For system administrators, mail is very useful because managers can use mail to write scripts and send memos to system users on a regular basis.

Parameters:
I ignore tty interrupt signals. (Interrupt)
I forced the interaction mode. (Interactive)
V prints a message, such as the location and status of the mail. (Verbose)
N does not read the mail. RC configuration file.
S mail title.
C CC email address.
B. bcc email address.
Example:
To send a letter to one or more email addresses, the user must enter the title and content of the letter because no other options are added. If user2 does not have a host location, it is sent to the user2 user on the email server.

Mail user1@email.address
Mail user1@email.address user2
Send mail.txt content to user2 and CC to user1. If you set this line of command to cronjob, You can regularly send the memorandum to the System user.
Mail-s title-C user1 user2 <mail.txt
Command: mesg
Permission: All Users
Usage: mesg [Y | n]
Determines whether to allow others to send messages to their terminal interfaces.
Count
Y: Allows messages to be transmitted to the terminal interface.
N: do not allow messages to be transmitted to the terminal interface.
If this parameter is not set, the message is transmitted. Otherwise, the current status of the Terminal interface is determined.
Example:
Change the current message settings to not allow the message to be uploaded to the terminal interface:
Mesg n
Mesg-related Commands include talk, write, and wall.
Name:/etc/aliases
Permission: System Administrator
Usage: newaliases
Note:
Sendmail uses a file in/etc/aliases for user name conversion. When Sendmail receives a message to XXX, it sends it to another user based on the content in the aliases file. This function can create a user that is only valid in the mail system. For example, mailing list will use this function, in mailinglist, we may create a mailinglist called redlinux@link.ece.uci.edu, but in fact there is no redlinux user. The actual content of the aliases file is to receive all the messages sent to this user.
The mailing list processing program is responsible for delivery.
/Etc/aliases is a text file. Sendmail requires/etc/aliases. DB in binary format. The function of newaliases is to convert/etc/aliases into a database that Sendmail can understand.

Parameter: No parameter. Example:
# Newaliases
The following command will do the same thing,
# Sendmail-Bi
Related commands:
Mail, mailq, newaliases, Sendmail
Name: Talk
Permission: All Users
Usage:
Talk person [ttyname]
Views with other users
Calculation:
Person: the user account that you want to talk to. If the user is on another machine, you can enter the person@machine.name
Ttyname: if the user has more than two tty connections at the same time, you can select a suitable tty to send messages.
Example. 1:
When talking to the user rollaend on the current machine, the rollaend has only one line:
Talk rollaend
The next step is to wait for rollaend to respond. If rollaend accepts the response, rollaend enters 'talk jzlil' to start the discussion. Press Ctrl + C to end the discussion.
Example 2: Use pts/2 To Talk To rollaend users on linuxfab. CX:
Talk Rollaend@linuxfab.cx pts/2
The next step is to wait for the rollaend response, if rollaend accept, then rollaend input 'talk jzlee@jzlee.home 'to start the discussion, press Ctrl + c

Note: If the text on the screen is abnormal, press Ctrl + L to update the screen.
Name: Wall
Permission: All Users
Usage:
Wall [Message]
Instructions for use:
Wall will send the message to the online users who set the mesg to yes. When the terminal interface is used as the standard input, the EOF (usually Ctrl + d) must be added at the end of the message)
Example:
Send the message "hi" to each user:
Wall hi
Name: Write
Permission: All Users
Usage:
Write user [ttyname]
Description: transmits messages to other users.
Calculation:
User: the user account for which the message is to be sent
Ttyname: if the user has more than two tty connections at the same time, you can select a suitable tty to send messages.
Example. 1:
Send a message to rollaend. At this time, rollaend has only one line:
Write rollaend
Press Ctrl + c
Example 2: Send a message to rollaend. The rollaend connections include pts/2 and pts/3:
Write rollaend pts/2
Press Ctrl + c
Note: If the recipient sets mesg n, the agent will not be able to pass it to the other party at this time.
Name: Kill
Permission: All Users
Usage:
Kill [-S Signal |-p] [-A] PID...
Kill-L [Signal]
Note: Kill sends a specific signal (signal) to the stroke ID of PID according to the specific action of the signal. If not specified, the preset is to send the signal of the termination (TERM ).

Count
-S (signal): The available signals include HUP (1), kill (9), and term (15), which respectively indicate focusing on running, cutting off, and ending; for detailed signals, kill-l can be used.

-P: The PID is printed and no signal is sent.
-L (signal): lists all available signal names
Example:
Cut the stroke (kill) with a PID of 323 ):
Kill-9 323
Re-run (restart) a stroke with a PID of 456 ):
Kill-HUP 456
Name: Nice
Permission: All Users
Usage: Nice [-N adjustment] [-adjustment] [-- adjustment = adjustment] [-- help] [-- version] [Command [arg...]

Note: The program is executed in the changed priority order. If no program is specified, the current priority order is printed, and the preset adjustment is 10, range:-20 (highest priority) to 19 (lowest priority)

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-N adjustment,-adjustment, -- adjustment = adjustment: Add adjustment to the original priority
-- Help: Display help messages
-- Version: displays version information.
Example:
Add 1 to the priority of LS and execute:
Nice-N 1 ls
Add 10 to the LS priority and execute:
Nice ls will add 10 to the LS priority and execute
Note: priority is the parameter used by the job system to determine CPU allocation. Linux uses the round-robin algorithm for CPU scheduling. The higher the priority, the more CPU time you may obtain.

Name: PS
Permission: All Users
Usage: PS [Options] [-- help]
Views: displays the dynamics of the instantaneous process.
Parameters:
There are many PS parameters. Only a few common parameters are listed here and their meanings are briefly described.
-A: list all the itineraries.
-W display widening can display more information
-Au displays more detailed information
-Aux: Show All itineraries containing other users
Au (x) output format:
User PID % CPU % mem vsz RSS tty stat Start Time Command
User: trip owner
PID: PID
% CPU: CPU usage
% Mem: memory usage
Vsz: Virtual Memory Used
RSS: memory used
TTY: the secondary device Number of the terminal (minor device Number of TTY)
Stat: the status of the trip:
D: Non-disruptive static operations (I/O operations through □□ B)
R: Execution in progress
S: static
T: Pause execution
Z: it does not exist but cannot be eliminated for the moment.
W: insufficient memory paging allocable
<: High-priority itinerary
N: low-priority itinerary
L: memory is allocated by PAGE and locked in the memory (instant system or memory a I/O)
Start: Start Time of the trip
Time: execution time
Command: The executed command.
Example:
PS
PID tty time cmd
2791 ttyp0 00:00:00 tcsh
3092 ttyp0 00:00:00 PS
% PS-
PID tty time cmd
1? 00:00:03 init
2? 00:00:00 kflushd
3? 00:00:00 kpiod
4? 00:00:00 kswapd
5? 00:00:00 mdrecoveryd
.......
% PS-Aux
User PID % CPU % mem vsz RSS tty stat Start Time Command
Root 1 0.0 0.7 1096 472? S sep10 0: 03 init [3]
Root 2 0.0 0.0 0 0? SW sep10 0: 00 [kflushd]
Root 3 0.0 0.0 0 0? SW sep10 0: 00 [kpiod]
Root 4 0.0 0.0 0 0? SW sep10 0: 00 [kswapd]
........
Name: pstree
Permission: All Users
Usage:
Pstree [-A] [-C] [-H |-hpid] [-L] [-N] [-p] [-u] [-G |-u] [PID | user]
Pstree-V
Note: All the itineraries are displayed in a tree chart. The tree chart is based on the PID (if specified) or the init (Root). If a user ID is specified, the tree Chart Only displays the user's itinerary.

Parameters:
-A shows the complete instructions and parameters for the itinerary. If the itinerary is replaced by memory, brackets will be added.
-C if there is a duplicate itinerary name, it will be listed separately (the default value will be added before *
Example:
Pstree
Init-+-AMD
|-Apmd
|-ATD
|-HTTPd --- 10 * [httpd]
% Pstree-P
Init (1)-+-AMD (1, 447)
|-Apmd (105)
|-ATD (339)
% Pstree-C
Init-+-AMD
|-Apmd
|-ATD
|-Httpd-+-HTTPd
|-HTTPd
|-HTTPd
|-HTTPd
....
Name: renice
Permission: All Users
Usage: renice priority [[-p] PID...] [[-G] pgrp...] [[-u] user...]
Note: Re-specify the priority of one or more processes (one or more based on the parameters)
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-P pid: Re-specify the priority of the stroke with the ID of the stroke as the PID
-G pgrp re-specifies the priority of the trip (one or more) with the ID of the Process Group as pgrp.
-U user re-specifies the priority of a trip with the itinerary owner as the user
Example:
Add 1 to the priority number of daemon and root for the itinerary with the itinerary ID 987 and 32:
Renice + 1 987-U daemon root-p 32
Note: Each process has a unique (unique) ID.
Name: Top
Permission: All Users
Usage: Top [-] [d delay] [Q] [C] [s] [s] [I] [N] [B]
Description: displays the Process status in real time.
Count
D: Change the display update speed, or press s in the interactive command Column
Q: there is no delay in display speed. if the user has the superuser permission, top will be executed in the highest priority.
C: Switch the display mode. There are two modes: one is to display only the name of the execution file, and the other is to display the complete path and name s: accumulative mode, the CPU time of the completed or deduplicated sub-itinerary (dead child process) is accumulated.

S: security mode. Cancel negotiated commands to avoid potential crisis.
I: Do not display any idle (idle) or useless (zombie) itinerary
N: number of updates. After the update is completed, the system will exit the top
B: The batch file mode, used together with the "N" parameter, can be used to output the top result to the file.
Example:
It is displayed that the system exits after 10 updates;
Top-N 10
The user will not be able to use the negotiated command to run the following commands on the itinerary:
Top-S
Input the result of the second update display to the file named top. log:
Top-N 2-B <top. Log
Name: Skill
Permission: All Users
Usage: Skill [signal to send] [Options] Select Program rules
Note:
Send a signal to the executing program. The preset message is term (interrupted). The commonly used messages are hup, Int, kill, stop, cont, and 0.
There are three ways to write messages:-9,-sigkill, and-kill. You can use-l or-L to list available messages.
General parameters:
-F Fast mode/not completed
-I interaction mode/each action is to be confirmed
-V: Detailed output/list information of the selected Program
-W smart warning message/not completed
-N no action/show program code
Parameter: the rule for selecting a program can be the terminal code, user name, program code, and command name.
-T Terminal code (TTY or PTY)
-U User Name
-P program code (PID)
-C command name:
The following lists known signal names, signal codes, and functions.
Name (CODE) function/Description
Alrm 14 exit
Hup 1 quit
Int 2 exit
Kill 9 exit/force close
Pipe 13 quit
Poll left
Prof leaves
Term 15 exit
Usr1 left
Usr2 left
Leave vtalrm
Stkflt exit/Only applicable to i386, m68k, arm, and PPC hardware
Unused exit/Only applicable to i386, m68k, arm, and PPC hardware
Tstp stops/generates content-related behaviors
Ttin stops/generates content-related behaviors
Ttou stop/generate content-related behaviors
Stop stop/force close
Cont restarts/if it is in the stopped status, it is restarted; otherwise, it is ignored.
PWR ignore/will leave in some systems
Ignore Winch
Chld ignore
Abrt 6 Core
FPE 8 core
Ill 4 Core
Quit 3 Core
Segv 11 core
Trap 5 Core
Sys Core/perhaps not yet implemented
EMR Core/perhaps not yet implemented
Bus Core/Core failure
Xcpu Core/Core failure
Xfsz Core/Core failure
Example:
Stop all programs on the Pty Device
Skill-kill-V pts /*
Stop three users: user1, user2, and user3
Skill-Stop user1 user2 user3
Other related commands: Kill
Name: expr
Permission: All Users
### String Length
Shell> expr length "this is a test"
14
### Digital business count
Shell> expr 14% 9
5
### Capture strings from locations
Shell> expr substr "this is a test" 3 5
Is is
### Number string only the first character
Shell> expr Index "testforthegame" E
2
### True string Reproduction
Shell> expr quote thisisatestformela
Thisisatestformela
Name: TR
### 1. For example, if you want to replace all the upper-case file names in the directory with lower-case file names?
There seems to be many ways, "TR" is one of them:
#! /Bin/sh
Dir = "/tmp/testdir ";
Files = 'Find $ Dir-type F ';
For I in $ files
Do
Dir_name = 'dirname $ I ';
Ori_filename = 'basename $ I'
New_filename = 'echo $ ori_filename | tr [: Upper:] [: lower:] '>/dev/NULL;
# Echo $ new_filename;
MV $ dir_name/$ ori_filename $ dir_name/$ new_filename
Done
### 2. self-testing... lowercase to uppercase
Tr abcdef... [del] ABCDE... [del]
Tr A-Z A-Z
Tr [: lower:] [: Upper:]
Shell> echo "this is a test" | tr a-Z A-Z> WWW
Shell> CAT WWW
This is a test
### 3. remove unwanted strings
Shell> tr-d This ### remove the relevant T. E. S. t
This
Man
Man
Test
E
### 4. Replace the string
Shell> tr-s "this" "test"
This
Test
Th
Te
Command: Clear
Purpose: Clear the screen.
Usage: enter clear on the console.
Name: reset, tset
Usage: tset [-iqqrs] [-] [-e CH] [-I ch] [-K CH] [-M mapping] [terminal]
Instructions for use:
Reset is actually the same command as tset. It is used to set the status of the terminal. Generally, this command automatically determines the type of the current terminal from the environment variable, command column, or other configuration files. If the specified type is? This program requires the user to enter the terminal type.

Because this program will set the terminal machine back to the original state, in addition to being used in login, when the system terminal enters some strange state because the program is not normally executed, you can also use it to reset the terminal. For example, if you accidentally use Cat commands to import binary files to the terminal, some terminals usually do not respond to keyboard input or some strange character problems. In this case, you can use reset to restore the terminal to the original state. Option description:

-P
Display the terminal category on the screen, but do not set the action. This command can be used to obtain the category of the current terminal.
-E ch
Set erase characters to Ch
-I ch
Set the delimiter to Ch.
-K ch
Set the character of a row to Ch.
-I
Do not set the action. If option-Q is not used, the current values of erase, interrupt, and delete characters will still be sent to the screen.
-Q
Do not display the values of erase, interrupt, and delete characters on the screen.
-R
Print the terminal category on the screen.
-S
Send the command used to set the term to the terminal in the string type, which is usually used in. login or. profile.
Example:
Let the user enter a terminal type and set the terminal to the preset status of this type.
# Reset?
Set erase characters to control-H
# Reset-e ^ B
Display the set strings on the screen
# Reset-S
Erase is control-B (^ B ).
Kill is control-U (^ U ).
Interrupt is control-C (^ C ).
Term = xterm;
Name: Compress
Permission: All Users
Usage: compress [-dfvcv] [-B maxbits]
Note:
Compress is a fairly old Unix File compression command. After compression, A. Z extension file name will be added to the compressed file to distinguish uncompressed files. The compressed file can be decompressed with uncompress. To Compress several files into one compressed file, you must first tar the file and then compress it. Since gzip can produce a better compression ratio, most people have switched to gzip as the archive compression tool.

Parameters:
C output result to standard output device (usually screen)
F. Write the file forcibly. If the target file already exists, it will be overwritten (force)
V prints program execution messages on the screen (verbose)
B sets the upper limit of the number of common strings. It is calculated in bits and can be set to 9 to 16 bits. Because the larger the value, the more common strings can be used and the larger the compression ratio, the default value 16 bits (BITs) is generally used)

D. decompress the compressed file.
V. List version information
Example:
Compress source. dat to source. dat. Z. If source. dat. Z already exists, the content will be overwritten by the compressed file.
Compress-f Source. dat
Compress source. dat to source. dat. Z and print the compression ratio.
-V and-F can be used together.
Compress-VF source. dat
After the compressed data is output, import target. dat. Z to change the compressed file name.
Compress-C source. dat> target. dat. Z
-The larger the value of B, the larger the compression ratio. The value range is 9-16 and the default value is 16.
Compress-B 12 source. dat
Decompress source. dat. Z to source. dat. If the file already exists, Press Y to overwrite the file. If you use the-DF program, the file is automatically overwritten. Because the system automatically adds. Z as the extension file name, source. dat is automatically treated as source. dat. Z.

Compress-D source. dat
Compress-D source. dat. Z
Name: LPD
Permission: All Users
Usage: LPD [-L] [# port]
LPD is a resident printer manager that manages local or remote Printers Based on/etc/printcap content. Each printer defined in/etc/printcap must have a corresponding directory in/var/lpd. Files starting with CF in the directory indicate a print table waiting to be sent to the appropriate device. This file is usually generated by LPR.

LPR and LPD form a system that can work offline. When you use LPR, the printer does not need to be available immediately or even do not exist. The lpd automatically monitors the printer status. When the printer goes online, the file is immediately sent for processing. All the applications do not have to wait for the printer to finish the previous job.

Parameters:
-L: display some debugging messages on the standard output.
# Port: Generally, lpd uses getservbyname to obtain the appropriate TCP/IP Port. You can use this parameter to force LPD to use the specified port.
Example:
This program is usually executed by programs in/etc/rc. d at the start of the system.
Name lpq
-- Display unfinished work usage in the hosts storage Column
Lpq [l] [p] [user]
Description
Lpq displays unfinished projects in the hosts storage column managed by LPD.
Example
Example 1. Show all operations in the LP Host Storage Column
# Lpq-plprank owner job files total size1st root 238 (standard input) 1428646 bytes

Related functions
LPR, LPC, lpd
Name: LPR
Permission: All Users
Usage: LPR [-P printer]
The printer manager lpd will send the file to the appropriate program or device for processing later. LPR can be used to send materials to local or remote hosts for processing.

Parameters:
-P printer: send data to the specified printer. The default value is LP.
Example:
Send www. C and KKK. C to the printer LP.
LPR-PLP www. c KKK. c
Name: lprm
-- Remove a job from the printer storage Column
/Usr/bin/lprm [p]
Description
Unfinished printer work will be placed in the printer storage column, this command can be used to cancel work that is often not sent to the printer. Since each printer has an independent storage column, you can use the-p command to set the printer to be used. If no printer is set, the preset printer is used.

This command checks whether the user has sufficient permissions to delete the specified file. Generally, only the file owner or system administrator has this permission.
Example
Remove job 1,123rd from the printer hpprinter
Lprm-phpprinter 1123
Remove job 1,011st from the preset printer
LPR 1011
Name: fdformat
Permission: All Users
Usage: fdformat [-N] Device
Instructions for use:
Low-level formatting of the specified drive device. When formatting a disk using this command, it is best to specify a device like the following:
/Dev/fd0d360 drive a: the disk size is kb.
/Dev/fd0h1440 drive a: the disk size is 1.4 MB.
/Dev/fd1h1200 drive B: the disk size is 1.2 MB.
If a device such as/dev/fd0 is used and the disk in it is not of the standard capacity, formatting may fail. In this case, you can use the setfdprm command to specify the required parameters first.
Parameters:
-N: Disable the validation function. This option will disable the validation step after formatting.
Example:
Fdformat-N/dev/fd0h1440
Format the disk a disk to a 1.4 MB disk. The validation steps are omitted.
Name: mformat
Permission: All Users
Usage:
Mformat [-T cylinders] [-H heads] [-s sectors] [-l volume_label] [-F] [-I fsver-sion] [-s sizecode] [-2 CATEGORY] [-M software_sector_size] [-A] [-x] [-C] [-H hidden_sectors] [-r root_sectors] [-B boot_sector] [-0 rate_on_track_0] [-A rate_on_other_tracks]
[-1] [-K] Drive:
Create a DOS file system on a low-level formatted disk. If the use_2m parameter is opened during mtools compilation, some parameters related to the 2 M format will take effect. Otherwise, these parameters (such as S, 2, 1, and m) will not work.

Parameters:
-T magnetic column (synlider) count
-H head count
-S: The number of magnetic zones for each Magnetic Track
-L tag
-F format the disk to FAT32, but this parameter is still in the experiment.
-I sets the version number in FAT32. Of course, this is still in the experiment.
-S: The size code of the magnetic area. The calculation method is sector = 2 ^ (size code + 7)
-Number of magnetic zones of the C magnetic bundle (cluster. If the given number causes the number of magnetic bundle to exceed the limit of the fat table, mformat will automatically enlarge the number of magnetic segments.
-S
-M: size of the soft magnetic zone. This number is the size of the magnetic zone in which the system returns. It is usually the same as the actual size.
-If a adds this parameter, mformat will generate a set of Atari system serial numbers for this disk.
-X format the disk into xdf format. Before use, you must use the xdfcopy command to perform low-level formatting on the disk.
-C generates a disk image that can install the MS-DOS file system ). Of course, this parameter is meaningless for a physical drive.
-H indicates the number of hidden magnetic areas. This is usually applicable when formatting the hard drive partition, because there is usually a partition table before the partition. This parameter is not tested and does not need to be used.
-N disk number
-The size of the r root directory, in the unit of disk space. This parameter is only valid for fat12 and fat16.
-B uses the specified file or device's boot magnetic area as the boot magnetic area of this disk or shard. Of course, the hardware parameters will change accordingly.
-K tries its best to keep the original boot magnetic zone.
-0: data transmission rate of The 0th track
-A data transfer rate out of track 0th
-2 Use 2 M format
-1 does not use the 2 M format
Example:
Mformat:
This will format the disk in A: (/dev/fd0) with the default value.
Name: mkdosfs
Permission: All Users
Usage: mkdosfs [-c |-l filename]
[-F number_of_fats]
[-F fat_size]
[-I volume_id]
[-M message_file]
[-N volume_name]
[-R root_dir_entry]
[-S sector_per_cluster]
[-V]
Device
[Block_count]
Note: Create a DOS file system. Device refers to the device code you want to establish a DOS file system. Such as/dev/hda1. Block_count indicates the number of blocks you want to configure. If block_count is not specified, the system automatically calculates the number of blocks that match the device size for you.

Parameters:
-C check whether there is any bad track before establishing the file system.
-L read the bad track records from the specified files.
-F specifies the number of file configuration tables (fat, File Allocation Table. The default value is 2. Currently, Linux's fat file system does not support more than two fat tables. This usually does not need to be changed.

-F specifies the size of the fat table, usually 12 or 16-bit tuples. The 12-bit tuples are usually used for disk disks, and the 16-bit tuples are used for the partition of General hard disks, that is, the so-called fat16 format. This value is usually selected by the system itself. Fat16 on a disk usually does not work, and fat12 on a hard disk.

-I specifies the volume ID. Generally, it is a number with four tuples, such as 2e203a47. If you do not give it to the system, it will be generated by yourself.
-M when the user tries to use this disk or Shard to start the system, but there is no operating system on it, the system will give the user a warning message. This parameter is used to change the message. You can edit the file with this parameter or use

-M-
In this way, the system requires you to enter the text directly. Note that the string length in the file must not exceed 418 characters, including the expanded tab and line feed characters (line breaks are counted as two characters under DOS !)

-N indicates the volume name, which is the disk label. Like the format command under DOS, it can be left empty. No preset value.
-R specifies the maximum number of files under the root directory. The number of files includes directories. The default value is 112 or 224 on the disk and 512 on the hard drive. Don't change this number.
-S indicates the number of magnetic zones of each magnetic cluster. It must be the power of 2. However, unless you know what you are doing, do not give this value randomly.
-V provides additional information

Example:
Mkdosfs-N tester/dev/fd0 format the disk in the slot to DOS format and set the tag to Tester