User:Altro971
Command-line interpreter
In computing, a command is a directive to a computer program to perform a specific task.
It may be issued via a command-line interface, such as a shell, or as input to a network service as part of a network protocol, or as an event in a graphical user interface triggered by the user selecting an option in a menu.
Basic Linux Commands
● ls - Lists directory contents.
● cd - Changes the current directory.
● pwd - Displays the present working directory.
● cat - Concatenates and displays files.
● echo - Displays arguments to the screen.
● man - Displays the online manual.
● exit - Exits the shell or your current session.
● clear - Clears the screen.
Directory tree
a directory contained inside another directory is called a sub directory. The terms parent and child are often used to describe the relationship between a sub directory and the directory in which it is cataloged, the latter being the parent. The top-most directory in such a file system, which does not have a parent of its own, is called the root directory.
Example : 1 directories, 6 files
path/to/folder/ ├── a-first.html ├── b-second.html ├── subfolder │ ├── readme.html │ ├── code.cpp │ └── code.h └── z-last-file.html
ls(list_Unix)
ls is a command to list computer files in Unix and Unix-like operating systems
Usage
The most common options to reveal this information or change the list of files are:
· -l long format, · -f do not sort. Useful for directories containing large numbers of files. · -F appends a character revealing the nature of a file, for example, * for an executable, or / for a directory. Regular files have no suffix. · -a lists all files in the given directory, including "." (which are hidden files in Unix). · -R recursively lists sub directories. The command ls -R / would therefore list all files. · -d shows information about a symbolic link or directory. · -t sort the list of files by modification time. · -h print sizes in human readable format. (e.g., 1K, 234M, 2G, etc · -1 (the numeric digit one) force output to be one entry per line.
File Permission:Decoding ls -l Output
$ ls -l
-rw-rw-r-- 1 jason users 10400 Sep 27 08:52 sales.data
Permissions -rw-rw-r--
Number of links 1
Owner name jason
Group name users
Number of bytes in the file 10400
Last modification time Sep 27 08:52
File name sales.data
Symbolic
notation |
Numeric
notation |
English |
----------
|
0000 | no permissions |
-rwx------
|
0700 | read, write, & execute only for owner |
-rwxrwx---
|
0770 | read, write, & execute for owner and group |
-rwxrwxrwx
|
0777 | read, write, & execute for owner, group and others |
---x--x--x
|
0111 | execute |
--w--w--w-
|
0222 | write |
--wx-wx-wx
|
0333 | write & execute |
-r--r--r--
|
0444 | read |
-r-xr-xr-x
|
0555 | read & execute |
-rw-rw-rw-
|
0666 | read & write |
-rwxr-----
|
0740 | owner can read, write, & execute; group can only read; others have no permissions |
Example:
d(rwx)r--rw-
|
·d : drafts is a directory (denoted by the file descriptor d). ·rwx: the owner (user) has the right to read (r), write (w) and execute (x). ·rw-: group members (users part of the editors group) have read and write (w) permissions;execute are not permitted. ·r--: others (users aside from the owner or members of editors) have read-only permissions; write and execute are not permitted, as denoted by the hyphen characters (-).
cd (command)
The cd
command, also known as chdir
(change directory)
Usage
user@wikipedia:~$ ls workreports games encyclopedia text.txt user@wikipedia:~$ cd games user@wikipedia:~/games$
A similar session in DOS (though the concept of a "home directory" may not apply, depending on the specific version) would look like this:
C:\> dir workreports <DIR> Wed Oct 9th 9:01 games <DIR> Tue Oct 8th 14:32 encyclopedia <DIR> Mon Oct 1st 10:05 text txt 1903 Thu Oct10th 12:43 C:\> cd games C:\games>
Pwd
Unix examples[edit]
Command
|
Explanation |
pwd
|
Display the current working directory. Example: /home/foobar |
pwd -P
|
Display the current working directory physical path - without symbolic link name, if any. Example: If standing in a dir /home/symlinked, that is a symlink to /home/realdir, this would show /home/realdir |
pwd -L
|
Display the current working directory logical path - with symbolic link name, if any. Example: If standing in a dir /home/symlinked, that is a symlink to /home/realdir, this would show /home/symlinked |
Help commands
Man is used to display documentation.
● $PATH controls your search path.
● Learn the full path to commands with which.
● Ask commands for help with --help or -h.
● Search man pages by using man -k.
Apropos (Unix) or man -k
apropos - search the manual page names and descriptions
Sample usage
The following example demonstrates the output of the apropos
command:
$ apropos mount free (1) - Display amount of free and used memory in the system mklost+found (8) - create a lost+found directory on a mounted Linux second extended file system mount (8) - mount a file system mountpoint (1) - see if a directory is a mountpoint ntfsmount (8) - Read/Write userspace NTFS driver. sleep (1) - delay for a specified amount of time switch_root (8) - switch to another filesystem as the root of the mount tree. umount (8) - unmount file systems
regexp keyword (abc.n) and a regular keyword:
$ apropos abc.n xzless XTestGrabControl (3) - XTest extension functions xzless (1) - view xz or lzma compressed (text) files
man page
A man page (short for manual page) is a form of software documentation usually found on a Unix or Unix-like operating system. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts. A user may invoke a man page by issuing the man
command.
Command usage
To read a manual page for a Unix command, a user can type:
man <command_name>
Creating and Removing Directories
mkdir [-p] directory - Create a directory.
rmdir [-p] directory - Remove a directory.
rm -rf directory - Recursively removes directory.
Displaying the Contents of Files
cat file
Display the contents of file.
more file
Browse through a text file.
less file
More features than more.
head file
Output the beginning (or top) portion of file.
tail file
Output the ending (or bottom) portion of file.
The Vi Editor
vi [file] Edit file.
vim [file] Same as vi, but more features.
view [file] Starts vim in read-only mode.
Vi Line Mode
:w Writes (saves) the file.
:w! Forces the file to be saved.
:q Quit.
:q! Quit without saving changes.
:wq! Write and quit.
:x Same as :wq.
Emacs
● Emacs is Powerful editor.
● Some people prefer vi, other emacs.
● Either are great editors.
● Use what feels comfortable to you.
emacs [file] Edit file.
C-<char> Ctrl while pressing <char>.
M-<char> "Meta" key (alt key) while
pressing <char>.
M-<char> Esc, then type <char>
Graphical Editors
● emacs Emacs has a graphical mode too.
● gedit The default text editor for Gnome.
● gvim The graphical version of vim.
● kedit The default text editor for the KDE.
● AbiWord Microsoft Word alternative.
● LibreOffice Full office suite.
● Kate Source code editor.
Summary
● Various graphical editors exist for Linux.
● Graphical modes exist for emacs and vi.
its function to concatenate files
Examples
Command | Explanation |
cat file1.txt | Display contents of file |
cat file1.txt file2.txt | Concatenate two text files and display the result in the terminal |
cat file1.txt file2.txt > newcombinedfile.txt | Concatenate two text files and write them to a new file |
cat >newfile.txt | Create a file called newfile.txt. Type the desired input and press CTRL+D to finish. The text will be in file newfile.txt. |
cat -n file1.txt file2.txt > newnumberedfile.txt | Some implementations of cat, with option -n, can also number lines |
cat file1.txt > file2.txt | Copy the contents of file1.txt into file2.txt |
cat file1.txt >> file2.txt | Append the contents of file1.txt to file2.txt |
sort > test4 | Concatenate the files, sort the complete set of lines, and write the output to a newly created file |
less | Run the program "less" with the concatenation of file1 and file2 as its input |
cat | Cancel "command" special behavior (e.g. paging) when it writes directly to TTY (cf. UUOC below) |
vim - Vi IMproved, a programmers text editor
It can be used to edit all kinds of plain text.It is especially useful for editing programs.
SYNOPSIS vim [options] [file ..] vim [options] - vim [options] -t tag vim [options] -q [errorfile] ex gex view gvim gview vimx evim eview rvim rview rgvim rgview
example:
$ vi text.txt Press i or insert and type your text and click esc and enter :wq! for quit
caution
Another program may be editing the same file. If this is the case,be careful not to end up with two different instances of the same file when making changes.
If edit session for this file crashed use ":recover" or "vim -r text.txt"to recover the changes (see ":help recovery").If you did this already, delete the swap file ".text.txt.swp".
Deleting, Copying, Moving, and Renaming Files
● rm
● cp
● mv
● gzip
gzcat Concatenates compressed files.
zcat Concatenates compressed files.
● tar
copying files and directories
Usage
Copying a file to another file:
cp [-fHip][--] sourcefile targetfile
Copying file(s) to a directory
cp [-fHip] [--] sourcefile... targetdirectory
Copying a directory to a directory (-r or -R must be used)
cp -r|-R [-fHip] [--] sourcedirectory... targetdirectory
Examples
Creating a copy of a file in the current directory:
cp prog.c prog.bak
Copy two files in the current directory into another directory:
cp jones smith /home/nick/clients
Copy a file to a new file and preserve the modification date, time, and access control list associated with the source file:
cp -p smith smith.jr
Copy a directory, including all its files and subdirectories, to another directory:
cp -R /home/nick/clients /home/nick/customers
Mv(Unix)
mv (short for move) is a Unix command that moves one or more files or directories from one place to another.
SYNOPSIS mv [OPTION]... [-T] SOURCE DEST mv [OPTION]... SOURCE... DIRECTORY mv [OPTION]... -t DIRECTORY SOURCE... Rename SOURCE to DEST, or move SOURCE(s) to DIRECTORY.
Examples
Command | Explanation |
---|---|
mv myfile mynewfilename | renames 'myfile' to 'mynewfilename'. |
mv myfile subdir/myfile | moves 'myfile' to 'subdir/myfile' relative to the current directory |
mv myfile subdir | same as the previous command, filename is implied to be the same |
mv be.03 /mnt/bkup/bes | copies 'be.03' to the 'bes' directory of the mounted volume 'bkup', then 'be.03' is removed |
mv afile another mydir | moves multiple files to directory 'mydir' |
mv /var/log/*z ~/logs | This takes longer than expected if '/var' is on a different file system, as it frequently is, since files will be copied and deleted. The shell expands ~ to the user's home directory and treats * as a wildcard character. |
gzip(unix)
gzip, gunzip, zcat - compress or expand named files.
Compressed files can be restored to their original form using gzip -d or gunzip or zcat.
command to zip:
gzip <file_name>
command to unzip(decompress):
gzip -d <file_name>
tar(unix) --Archive
‘tar’ saves many files together into a single tape or disk archive, and can restore individual files from the archive.
EXAMPLES
tar -cf archive.tar foo bar # Create archive.tar from files foo and bar. tar -tvf archive.tar # List all files in archive.tar verbosely. tar -xf archive.tar # Extract all files from archive.tar. Main operation mode: -A, --catenate, --concatenate append tar files to an archive -c, --create create a new archive -d, --diff, --compare find differences between archive and file system --delete delete from the archive (not on mag tapes!) -r, --append append files to the end of an archive -t, --list list the contents of an archive --test-label test the archive volume label and exit -u, --update only append files newer than copy in archive -x, --extract, --get extract files from an archive
Wildcards
● A character or string used for pattern matching.
● Globbing expands the wildcard pattern into a list of files and/or directories. (paths)
● Wildcards can be used with most commands.(ls,rm,cp
)
Wildcards characters
● * - matches zero or more characters.
○ *.txt
○ a*
○ a*.txt
● ? - matches exactly one character.
○ ?.txt
○ a?
○ a?.txt
More Wildcards - Character Classes
● [] - A character class.
○ Matches any of the characters included between the brackets. Matches exactly one character.
○ [aeiou]
○ ca[nt]*
■ can
■ cat
■ candy
■ catch
More Wildcards - Character Classes
● [!] - Matches any of the characters NOT included between the brackets. Matches exactly one character.
○ [!aeiou]*
■ baseball
■ cricket
More Wildcards - Ranges
● Use two characters separated by a hyphen to
create a range in a character class.
● [a-g]*
○ Matches all files that start with a, b, c, d, e, f, or g.
● [3-6]*
○ Matches all files that start with 3, 4, 5 or 6.
Named Character Classes
● [[:alpha:]]
● [[:alnum:]]
● [[:digit:]]
● [[:lower:]]
● [[:space:]]
● [[:upper:]]
Matching Wildcard patterns
● \ - escape character. Use if you want to match
a wildcard character.
○ Match all files that end with a question mark:
■ *\?
● done?
Input/Output Types
standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution.
Standard Input stdin 0
Standard input is a stream from which a program reads its input data. The program requests data transfers by use of the read operation. Not all programs require stream input.
Standard Output stdout 1
Standard output is a stream to which a program writes its output data. The program requests data transfer with the write operation. Not all programs generate output. For example, the file rename command (variously called mv, move, or ren) is silent on success.
Standard Error stderr 2
Standard error is another output stream typically used by programs to output error messages or diagnostics. It is a stream independent of standard output and can be redirected separately.
Redirection
>
Redirects standard output to a file.
Overwrites (truncating) existing contents.
>> Redirects standard output to a file.
Appends to any existing contents.
<
Redirects input from a file to a command.
&
Used with redirection to signal that a file descriptor is being used.
2>&1
Combine stderr and standard output.
2>file
Redirect standard error to a file.
The Null Device
>/dev/null Redirect output to nowhere.
$ ls here not-here 2> /dev/null
here
$ ls here not-here > /dev/null 2>&1
Comparing the Contents of Files
diff file1 file2 Compare two files.
sdiff file1 file2 Side-by-side comparison.
vimdiff file1 file2 Highlight differences in vim.
Searching in Files and Using Pipes
● grep
● file
● cut
● tr
● column
● more
● less
● Pipes
Grep(unix)
grep
is a command-line utility for searching plain-text data sets for lines that match a regular expression.
command g/re/p (globally search for a regular expression and print matching lines)
It searches files for specified words or patterns
The grep command is case sensitive
To ignore upper/lower case distinctions, use the -i option, i.e. type
Sample usage
The following example demonstrates the output of the grep
command given different arguments
$ grep -i science science.txt
recursive grep
Contains$ grep -r -l "<to match>" --include="<wildcard for files>"
Doesn't Contain$ grep -r -L "<to match>" --include="<wildcard for files>"
Find Occurrences and output to CSV$ grep -r "<to match>" --include="<wildcard>" | cut -d : -f 1,3 | sed 's/: /,/g'
Find Occurrences and output to CSV with prepended string$ grep -r "<to match>" --include="<wildcard>" | cut -d : -f 1,3 | sed 's/: /,/g' | awk '{print "<prepend string>"$0}'
agrep (approximate grep) matches even when the text only approximately fits the search pattern.
This following invocation finds net masks in file my file, but also any other word that can be derived from it, given no more than two substitutions.
agrep -2 netmasks myfile
This example generates a list of matches with the closest, that is those with the fewest, substitutions listed first. The command flag B means best:
agrep -B netmasks myfile
file (command)-- determine file type
file tests each argument in an attempt to classify it. There are three sets of tests, performed in this order: file system tests, magic tests, language tests.
Classifies the named files according to the type of data they contain.
Examples
$ To report on all files in your home directory $file * LinkSource.txt: ASCII text, with CRLF line terminators Loc1: directory copytext.txt: ASCII text, with no line terminators
$ file file.c file.c: C program text
$ file program program: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), stripped
$ file /dev/hda1 /dev/hda1: block special (0/0)
$ file -s /dev/hda1 /dev/hda1: Linux/i386 ext2 filesystem
more
is a command to view (but not modify) the contents of a text file one screen at a time.
Usage(Unix)
more [options] [file_name]
If no file name is provided, more
looks for input from standard input.
less
used to view (but not change) the contents of a text file one screen at a time. It is similar to more
, but has the extended capability of allowing both forward and backward navigation through the file.
Users should realize that less provides more emulation plus extensive enhancements.
Usage
less [options] [file_name]
Frequently used options[edit]
-g
: Highlight just the current match of any searched string.-i
: Search case-insensitively.-m
: Show more detailed prompt, including file position.-N
: Show line numbers (useful for viewing source code).-x3
: Set tabstops (the number of columns per hard tab character) to the specified number (3, in this example) (useful for viewing source code).-S
: Disable line wrapping ("chop long lines"). Long lines can be seen by side-scrolling.-X
: Leave file contents on screen when less exits.-?
: Show help.--follow-name
: Follow mode, for log files that get replaced while being viewed
Examples
less -M readme.txt # Read "readme.txt" less +F /var/log/mail.log # Follow mode for log file * | less # Easier file analysis less -I -g void *.c # Case insensitive search for "void" in all .c files
Copying Files over the Network
● SCP - Secure copy
● SFTP - SSH file transfer protocol
● PuTTY Secure Copy client - pscp.exe
● PuTTY Secure File Transfer client - psftp.exe
Graphical SCP/SFTP Clients
● Cyberduck
● FileZilla
● WinSCP
scp / sftp command line utilities
scp source destination
Copy source to destination.
sftp host
Start a secure file transfer session with host.
sftp jason@host
ftp Command Line Utility
ftp host
Start a file transfer session with host.
Summary
● Transfer files using a client.
● Command line clients: scp, sftp, ftp.
● Graphical clients: Cyberduck, FileZilla.
● Use scp or sftp over ftp when possible.
Process Management
sudo
Top
Ps
sar
iostat
free
kill
who
df
du
id
sort
link
sudo(Unix)
security privileges of another user, by default the superuser
It originally stood for "superuser do"
Usage example
sudo su - wladmin ---> super user as web logic admin
Running ssh command:
sudo su - wladmin -c '/apps/xxx/xxx/xxxxxxx.cmd'
top (table of processes) is a task manager program, found in many Unix-like operating systems, that displays information about CPU and memory utilization.
SYNOPSIS
top -hv|-bcHiOSs -d secs -n max -u|U user -p pid -o fld -w [cols]
The traditional switches `-' and white space are optional. When operating top, the two most important keys are the help (h or ?) key and quit ('q') key. Alternatively, you could simply use the traditional interrupt key (^C) when you're done.
Startup Defaults
items shown with an asterisk (`*') could be overridden through the command-line. All are explained in detail in the sections that follow.
Global-defaults
Global-defaults A - Alt display Off (full-screen) * d - Delay time 1.5 seconds * H - Threads mode Off (summarize as tasks) I - Irix mode On (no, `solaris' smp) * p - PID monitoring Off (show all processes) * s - Secure mode Off (unsecured) B - Bold enable On (yes, bold globally)
Summary-Area-defaults
l - Load Avg/Uptime On (thus program name) t - Task/Cpu states On (1+1 lines, see `1') m - Mem/Swap usage On (2 lines worth) 1 - Single Cpu Off (thus multiple cpus)
Task-Area-defaults
b - Bold hilite Off (use `reverse') * c - Command line Off (name, not cmdline) * i - Idle tasks On (show all tasks) J - Num align right On (not left justify) j - Str align right Off (not right justify) R - Reverse sort On (pids high-to-low) * S - Cumulative time Off (no, dead children) * u - User filter Off (show euid only) * U - User filter Off (show any uid) V - Forest view On (show as branches) x - Column hilite Off (no, sort field) y - Row hilite On (yes, running tasks) z - color/mono On (show colors)
MAN TOP
---use manual command for info
Ps - (short for "process status")
ps displays information about a selection of the active processes. If you want a repetitive update of the selection and the displayed information, use top(1) instead.
EXAMPLES
To see every process on the system using standard syntax:
ps -e ps -ef ps -eF ps -ely
To print a process tree:
ps -ejH ps axjf
Users can also utilize the ps
command in conjunction with the grep
command to find information about a single process, such as its id:
$ # Trying to find the PID of `firefox-bin` which is 2701 $ ps -A | grep firefox-bin 2701 ? 22:16:04 firefox-bin
The use of pgrep
simplifies the syntax and avoids potential race conditions:
$ pgrep -l firefox-bin 2701 firefox-bin
To see every process running as root in user format:
# ps -U root -u USER PID %CPU %MEM VSZ RSS TT STAT STARTED TIME COMMAND root 1 0.0 0.0 9436 128 - ILs Sun00AM 0:00.12 /sbin/init --
sar (Unix)
System Activity Report (sar
):Collect, report, or save system activity information.
sar command is used to get the usage history of system resource such as CPU, RAM, SWAP, IO etc. /var/log/sa/ directory contains the information of system usage for the specified number of days as per OS configuration.
Syntax
sar [-flags] [ -e time ] [ -f filename ] [-i sec ] [ -s time ]
- -f
- filename Uses filename as the data source for sar. The default is the current daily data file /var/adm/sa/sadd.
- -e
- time Selects data up to time. The default is 18:00.
- -i
- sec Selects data at intervals as close as possible to sec seconds.
Example
[user@localhost]$ sar # Displays current CPU activity.
pgrep, pkill - look up or signal processes based on name and other attributes
pgrep looks through the currently running processes and lists the process IDs which match the selection criteria to stdout. All the criteria have to match. pkill will send the specified signal (by default SIGTERM) to each process instead of listing them on stdout.
example;
$ pgrep -u root sshd
will only list the processes called sshd AND owned by root. On the other hand,
$ pgrep -u root,daemon
will list the processes owned by root OR daemon.
iostat (input/output statistics) is a computer system monitor tool used to collect and show operating system storage input and output statistics.
The iostat command is used for monitoring system input/output device loading by observing the time the devices are active in relation to their average transfer rates. The iostat command generates reports that can be used to change system configuration to better balance the input/output load between physical disks.
Syntax and availability
iostat –x -
displays output where each line (row) gives numerical data for one device.
iostat -x 30 - It is best to run iostat
specifying a time interval in seconds
iostat –En -To check san storage external disk
iostat [ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -t ] [ -V ] [ -x ] [ -y ] [ -z ] [ -j { ID | LABEL | PATH | UUID | ... } ] [ [ -T] -g group_name ] [ -p [ device [,...] | ALL ] ] [ device [...] | ALL ] [ interval [ count ] ]
The iostat command generates two types of reports, the CPU Utilization report and the Device Utilization report.
Free (unix)
free - Display amount of free and used memory in the system
free displays the total amount of free and used physical and swap memory in the system, as well as the buffers and caches used by the kernel. The information is gathered by parsing /proc/meminfo.
example
wladmin@user# free -g total used free shared buff/cache available Mem: 15 11 1 0 2 3 Swap: 7 0 7
Usage: free [options] Options: -h, --human show human-readable output --si use powers of 1000 not 1024 -l, --lohi show detailed low and high memory statistics -t, --total show total for RAM + swap -s N, --seconds N repeat printing every N seconds -c N, --count N repeat printing N times, then exit -w, --wide wide output -V, --version output version information and exit
kill - terminate a process The command kill sends the specified signal to the specified process or process group.If no signal is specified, the TERM signal is sent.The TERM signal will kill processes which do not catch this signal. For other processes, it may be necessary to use the KILL (9) signal, since this signal cannot be caught.
kill -9 <process id>
Swap(Unix)
# swap -s ----To view the summary of the current swap space allocation total: 106256k bytes allocated + 8512k reserved = 114768k used, 587512k available
# swap –l --- To list details of the system’s virtual swap space: swapfile dev swaplo blocks free /dev/dsk/c0t0d0s1 136,1 16 1206736 1084736 /export/data/swapfile -16 40944 40944
who - show who is logged on
who [OPTION]... [ FILE | ARG1 ARG2 ]
Print information about users who are currently logged in.
-a, --all same as -b -d --login -p -r -t -T -u -b, --boot time of last system boot -d, --dead print dead processes -H, --heading print line of column headings
df (abbreviation for disk free) is a standard Unix command used to display the amount of available disk space for file systems
Example
The following is an example of the output of the df command.
$ df Filesystem 1024-blocks Free %Used Iused %Iused Mounted on /dev/hd4 32768 16016 52% 2271 14% / /dev/hd2 4587520 1889420 59% 37791 4% /usr /dev/hd9var 65536 12032 82% 518 4% /var /dev/hd3 819200 637832 23% 1829 1% /tmp /dev/hd1 524288 395848 25% 421 1% /home /proc - - - - - /proc /dev/hd10opt 65536 26004 61% 654 4% /opt
du (Unix): summarize disk usage
du
(abbreviated from disk usage) is a standard Unix program used to estimate file space usage—space used under a particular directory or files on a file system.
Usage
du
takes a single argument, specifying a path name for du to work; if it is not specified, the current directory is used
Examples
du [OPTION]... [FILE]... du [OPTION]... --files0-from=F
[OPTION] -S, --separate-dirs ->for directories do not include size of sub directories -s, --summarize ->display only a total for each argument
disk usage of all sub directories and files including hidden files within the current directory (sorted by reverse file size) : $ du -sk .[!.]* *| sort -nr
id
Return user identity
To check for user present are not
id -a <user name> : gives the details of the uid, gid, groups
id <user name> : gives the details of the uid, gid
sort (Unix)
prints the lines of its input or concatenation of all files listed in its argument list in sorted order
Syntax
sort [OPTION]... [FILE]...
With no FILE
, or when FILE
is -
, the command reads from standard input.
Parameters[edit]
-b | Ignores leading blanks. |
-d | Considers only blanks and alphanumeric characters. |
-f | Fold lower case to upper case characters. |
-g | Compares according to general numerical value. |
-i | Considers only printable characters. |
-M | Compares (unknown) < 'JAN' < ... < 'DEC'. |
-h | Compare human readable numbers (e.g., 2K 1G). |
-n | Compares according to string numerical value. |
-R | Shuffles, but groups identical keys. See also: shuf |
-r | Reverses the result of comparisons. |
passwd is used to change a user's password
An example record may be:
jsmith:x:1001:1000:Joe Smith,Room 1007,(234)555-8910,(234)555-0044,email:/home/jsmith:/bin/sh
The fields, in order from left to right, are:
1. jsmith
: User name
2. x
: Information used to validate a user's password;
3. 1001
: user identifier number, used by the operating system for internal purposes. It need not be unique.
4. 1000
: group identifier number, which identifies the primary group of the user
5. Room 1007...
: Gecos field, commentary that describes the person or account.
6. /home/jsmith
: Path to the user's home directory.
7. /bin/sh
: Program that is started every time the user logs into the system.
link (Unix)
link - call the link function to create a link to a file
link FILE1 FILE2 link OPTION
ln - make links between files-Create hard link by default.
ln [OPTION]... [-T] TARGET LINK_NAME (1st form)--create a link to TARGET with the name LINK_NAME ln [OPTION]... TARGET (2nd form)--create a link to TARGET in the current directory. ln [OPTION]... TARGET... DIRECTORY (3rd form)--create links to each TARGET in DIRECTORY ln [OPTION]... -t DIRECTORY TARGET... (4th form)--create links to each TARGET in DIRECTORY
symbolic Link
-s, --symbolic make symbolic links instead of hard links
pushd and popd
The pushd
command saves the current working directory in memory so it can be returned to at any time, optionally changing to a new directory.
Syntax
pushd [path | ..]
path
This optional command-line argument specifies the directory to make the current directory. If path
is omitted, the path at the top of the directory stack is used, which has the effect of toggling between two directories.
Popd
popd
Bourne shell
The Bourne shell (sh
) is a shell command-line interpreter for computer operating systems.
/bin/sh
—which will be the Bourne shell, or a symbolic link or hard link to a compatible shell—even when other shells are used by most users.
cap vs less & more Vs grep
Bash Variables
env | Show environment variables |
echo $NAME | Output value of $NAME variable |
export NAME=value | Set $NAME to value |
$PATH | Executable search path |
$HOME | Home directory |
$SHELL | Current shell |
File Operations
touch file1
Create file1 |
cat file1 file2
Concatenate files and output |
less file1
View and paginate file1 |
file file1
Get type of file1 |
cp file1 file2
Copy file1 to file2 |
mv file1 file2
Move file1 to file2 |
rm file1
Delete file1 |
head file1
Show first 10 lines of file1 |
tail file1
Show last 10 lines of file1 |
tail -F file1
Output last lines of file1 as it changes |
File Permission Numbers
First digit is owner permission, second is group and third is everyone. | |
Calculate permission digits by adding numbers below. | |
4 | read (r) |
2 | write (w) |
1 | execute (x) |
Pipes
cmd1 | cmd2
stdout of cmd1 to cmd2 |
cmd1 |& cmd2
stderr of cmd1 to cmd2 |
Process Management
ps | Show snapshot of processes |
top | Show real time processes |
kill pid | Kill process with id pid |
pkill name | Kill process with name name |
killall name | Kill all processes with names beginning name |
IO Redirection
cmd < file |
Input of cmd from file |
cmd1 <(cmd2) |
Output of cmd2 as file input to cmd1 |
cmd > file |
Standard output (stdout) of cmd to file |
cmd > /dev/null |
Discard stdout of cmd |
cmd >> file |
Append stdout to file |
cmd 2> file |
Error output (stderr) of cmd to file |
cmd 1>&2 |
stdout to same place as stderr |
cmd 2>&1 |
stderr to same place as stdout |
cmd &> file |
Every output of cmd to file |
cmd refers to a command. |
Pipes |
cmd1 | cmd2 |
stdout of cmd1 to cmd2 |
cmd1 |& cmd2 |
stderr of cmd1 to cmd2 |
Command Lists |
cmd1 ; cmd2 |
Run cmd1 then cmd2 |
cmd1 && cmd2 |
Run cmd2 if cmd1 is successful |
cmd1 || cmd2 |
Run cmd2 if cmd1 is not successful |
cmd & |
Run cmd in a subshell |
Bash Commands
Bash Shortcuts
Bash Variables
IO RedirectionPipesCommand Lists
|
Directory Operations
ls Options
Search Files
File Operations
Watch a Command
Process Management
|
Nano Shortcuts
Screen Shortcuts
File Permissions
File Permission Numbers
|
Command Lists
cmd1 ; cmd2
Run cmd1 then cmd2 |
cmd1 && cmd2
Run cmd2 if cmd1 is successful |
cmd1 || cmd2
Run cmd2 if cmd1 is not successful |
cmd &
Run cmd in a subshell |
1 – SYSTEM INFORMATION
# Display Linux system information uname -a # Display kernel release information uname -r # Show which version of redhat installed cat /etc/redhat-release # Show how long the system has been running + load uptime # Show system host name hostname # Display the IP addresses of the host hostname -I # Show system reboot history last reboot # Show the current date and time date # Show this month's calendar cal # Display who is online w # Who you are logged in as whoami
2 – HARDWARE INFORMATION
# Display messages in kernel ring buffer dmesg # Display CPU information cat /proc/cpuinfo # Display memory information cat /proc/meminfo # Display free and used memory ( -h for human readable, -m for MB, -g for GB.) free -h # Display PCI devices lspci -tv # Display USB devices lsusb -tv # Display DMI/SMBIOS (hardware info) from the BIOS dmidecode # Show info about disk sda hdparm -i /dev/sda # Perform a read speed test on disk sda hdparm -tT /dev/sda # Test for unreadable blocks on disk sda badblocks -s /dev/sda
3 – PERFORMANCE MONITORING AND STATISTICS
# Display and manage the top processes top # Interactive process viewer (top alternative) htop # Display processor related statistics mpstat 1 # Display virtual memory statistics vmstat 1 # Display I/O statistics iostat 1 # Display the last 100 syslog messages (Use /var/log/syslog for Debian based systems.) tail 100 /var/log/messages # Capture and display all packets on interface eth0 tcpdump -i eth0 # Monitor all traffic on port 80 ( HTTP ) tcpdump -i eth0 'port 80' # List all open files on the system lsof # List files opened by user lsof -u user # Display free and used memory ( -h for human readable, -m for MB, -g for GB.) free -h # Execute "df -h", showing periodic updates watch df -h
4 – USER INFORMATION AND MANAGEMENT
# Display the user and group ids of your current user. id # Display the last users who have logged onto the system. last # Show who is logged into the system. who # Show who is logged in and what they are doing. w # Create a group named "test". groupadd test # Create an account named john, with a comment of "John Smith" and create the user's home directory. useradd -c "John Smith" -m john # Delete the john account. userdel john # Add the john account to the sales group usermod -aG sales john
5 – FILE AND DIRECTORY COMMANDS
# List all files in a long listing (detailed) format ls -al # Display the present working directory pwd # Create a directory mkdir directory # Remove (delete) file rm file # Remove the directory and its contents recursively rm -r directory # Force removal of file without prompting for confirmation rm -f file # Forcefully remove directory recursively rm -rf directory # Copy file1 to file2 cp file1 file2 # Copy source_directory recursively to destination. If destination exists, copy source_directory into destination, otherwise create destination with the contents of source_directory. cp -r source_directory destination # Rename or move file1 to file2. If file2 is an existing directory, move file1 into directory file2 mv file1 file2 # Create symbolic link to linkname ln -s /path/to/file linkname # Create an empty file or update the access and modification times of file. touch file # View the contents of file cat file # Browse through a text file less file # Display the first 10 lines of file head file # Display the last 10 lines of file tail file # Display the last 10 lines of file and "follow" the file as it grows. tail -f file
6 – PROCESS MANAGEMENT
# Display your currently running processes ps # Display all the currently running processes on the system. ps -ef # Display process information for processname ps -ef | grep processname # Display and manage the top processes top # Interactive process viewer (top alternative) htop # Kill process with process ID of pid kill pid # Kill all processes named processname killall processname # Start program in the background program & # Display stopped or background jobs bg # Brings the most recent background job to foreground fg # Brings job n to the foreground fg n
7 – FILE PERMISSIONS
PERMISSION EXAMPLE U G W rwx rwx rwx chmod 777 filename rwx rwx r-x chmod 775 filename rwx r-x r-x chmod 755 filename rw- rw- r-- chmod 664 filename rw- r-- r-- chmod 644 filename # NOTE: Use 777 sparingly! LEGEND U = User G = Group W = World r = Read w = write x = execute - = no access
8 – NETWORKING
# Display all network interfaces and ip address ifconfig -a # Display eth0 address and details ifconfig eth0 # Query or control network driver and hardware settings ethtool eth0 # Send ICMP echo request to host ping host # Display whois information for domain whois domain # Display DNS information for domain dig domain # Reverse lookup of IP_ADDRESS dig -x IP_ADDRESS # Display DNS ip address for domain host domain # Display the network address of the host name. hostname -i # Display all local ip addresses hostname -I # Download http://domain.com/file wget http://domain.com/file # Display listening tcp and udp ports and corresponding programs netstat -nutlp
9 – ARCHIVES (TAR FILES)
# Create tar named archive.tar containing directory. tar cf archive.tar directory # Extract the contents from archive.tar. tar xf archive.tar # Create a gzip compressed tar file name archive.tar.gz. tar czf archive.tar.gz directory # Extract a gzip compressed tar file. tar xzf archive.tar.gz # Create a tar file with bzip2 compression tar cjf archive.tar.bz2 directory # Extract a bzip2 compressed tar file. tar xjf archive.tar.bz2
10 – INSTALLING PACKAGES
# Search for a package by keyword. yum search keyword # Install package. yum install package # Display description and summary information about package. yum info package # Install package from local file named package.rpm rpm -i package.rpm # Remove/uninstall package. yum remove package # Install software from source code. tar zxvf sourcecode.tar.gz cd sourcecode ./configure make make install
11 – SEARCH
# Search for pattern in file grep pattern file # Search recursively for pattern in directory grep -r pattern directory # Find files and directories by name locate name # Find files in /home/john that start with "prefix". find /home/john -name 'prefix*' # Find files larger than 100MB in /home find /home -size +100M
12 – SSH LOGINS
# Connect to host as your local username. ssh host # Connect to host as user ssh user@host # Connect to host using port ssh -p port user@host
13 – FILE TRANSFERS
# Secure copy file.txt to the /tmp folder on server scp file.txt server:/tmp # Copy *.html files from server to the local /tmp folder. scp server:/var/www/*.html /tmp # Copy all files and directories recursively from server to the current system's /tmp folder. scp -r server:/var/www /tmp # Synchronize /home to /backups/home rsync -a /home /backups/ # Synchronize files/directories between the local and remote system with compression enabled rsync -avz /home server:/backups/
14 – DISK USAGE
# Show free and used space on mounted filesystems df -h # Show free and used inodes on mounted filesystems df -i # Display disks partitions sizes and types fdisk -l # Display disk usage for all files and directories in human readable format du -ah # Display total disk usage off the current directory du -sh
15 – DIRECTORY NAVIGATION
# To go up one level of the directory tree. (Change into the parent directory.) cd .. # Go to the $HOME directory cd # Change to the /etc directory cd /etc
Q & A
How to search the file for specified word or keywords?