Linux Basic commands

Information about binary

whereis sendmail
which sendmail

Take program to background

ctrl+z

Bring to background

fg

superuser and exit

sudo su; exit;

login as another user without password

sudo -u user_name -s
sudo -u www-data -s

Copy Files, with symbolic links

Dont traverse symbolic link (copy symlink, not target) cp -P src dest
will traverse symbolic link cp src dest
will copy all symbolic link and dirs cp -RP
Make exact copy of source with -a cp -a src dest

File Write/Append

append

program >> file_name.ext strings "Coach.xlsx" >> "Coach.xlsx.strings.txt" echo "apple" >> apple.txt

write without append

program > file_name.ext strings "Coach.xlsx" > "Coach.xlsx.strings.txt"

sed

Find and Replace

 # sed 's/<FIND_PATTERN>/<REPLACE_PATTERN>/'
 # replace / by \/

# Replace "GET " and " HTTP/1.1 "
cat GET_SORT.txt | sed 's/GET //' | sed 's/ HTTP\/1.1//' > get_sort_sed.txt

File Information

$ file [option] [filename]
$ file -b -brief filename
$file directoryname/*
  all files info in dir
-i Mimetype
$ file -N *
  dont pad output i.e. no line break maybe

Readelf

*** We can see loadable segments in the output of the readelf program.
readelf -l vmlinux

Elf file type is EXEC (Executable file)
Entry point 0x1000000
There are 5 program headers, starting at offset 64

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000200000 0xffffffff81000000 0x0000000001000000 EP
                 0x0000000000893000 0x0000000000893000  R E    200000
  LOAD           0x0000000000a93000 0xffffffff81893000 0x0000000001893000
                 0x000000000016d000 0x000000000016d000  RW     200000
  LOAD           0x0000000000c00000 0x0000000000000000 0x0000000001a00000
                 0x00000000000152d8 0x00000000000152d8  RW     200000
  LOAD           0x0000000000c16000 0xffffffff81a16000 0x0000000001a16000
                 0x0000000000138000 0x000000000029b000  RWE    200000
=======
### Read Elf

// Read headers of elf file $readelf -h /usr/bin/sudo


##  File View

$ls | less | more | most less: scroll up and down, quit using q, vi key binding;
-r to display raw sequence
-R only ANSI escape char
-X (long form: --no-init [ wont clear screen ] (capital x) behave like more command / to find, n search forward, N search back !shell_command, execute something on shell $ ls | less $ !file someoutputline.txt

more: scroll forward only

wont clear screen

most: scroll up,dn, left right
-view multiple files
-pass raw escape sequence by default


### head

read 1KB head -c1K


### Opened files by process

List of opened file by a process is available via proc filesystem: $ sudo ls /proc/1/fd/ 0 10 12 14 16


### tail


## grep

grep pattern

Binary file (standard input) matches for non text file

Process a binary file as if it were text

grep -a 'pattern'

Grep with lines begin with GET and sort

cat getb.txt | grep -a "^GET" | sort > GET_SORT.txt


## Firewall

sudo ufw allow 21 sudo ufw allow ftp sudo service ufw restart


# Files
## Hex view of file

Hexdump -c


# proftpd  FTP server

get the latest update

sudo apt-get update

sudo apt-get upgrade will update installed packages

$ sudo apt-get install proftpd

$ sudo vi /etc/proftpd/proftpd.conf

DefaultRoot : Uncomment this line to restrict users with their home folders. RequireValidShell: Uncomment this line and make it “On” to enable logging in for users, even for those who doesn’t have a valid shell in /etc/shells to log in.

Since 1.3.0rc1 it's also possible to use the following:

DefaultAddress 192.168.10.30 my.domain.tld

Ec2 hosting

# If your host was NATted, this option is useful in order to
# allow passive tranfers to work. You have to use your public
# address and opening the passive ports used on your firewall as well.
# MasqueradeAddress             1.2.3.4
MasqueradeAddress ftp.somedomain.com

# In some cases you have to specify passive ports range to by-pass
# firewall limitations. Ephemeral ports can be used for that, but
# feel free to use a more narrow range.
PassivePorts                  49152 65534

Open port on ec2 network setting

80 0.0.0.0/0 is one example of opened for port 80
Similarly opening port 20-21 20-21 with dash
20-21 : maybe opening from port 20 to 21
49152-65534:

$ sudo service proftpd restart

Creating ProFTPD Users

sudo useradd myproftpduser
sudo passwd myproftpduser
sudo usermod -m -d /var/www/myproftpduser

Troubleshoot

/var/log/proftpd/proftpd.log

User and Groups

User List

$less /etc/passwd

Add new user

$sudo useradd ftp.user_name

https://linuxize.com/post/how-to-list-users-in-linux/

Delete User

userdel userName

// maybe delete user homa and mail
userdel -r userName

// Force delete
userdel -r -f tom

// Remove any SELinux user mapping 
userdel -Z -r -f jerry

https://www.cyberciti.biz/faq/linux-remove-user-command/

change password of user

$sudo passwd ftp.user_name

set user home directory

$ sudo usermod -m -d /var/www/user_name.com.sg ftp.user_name
    info message can be displayed if dir exists already, not error
        usermod: directory /var/www/user_name.com.sg exists

Add user to new group

$ sudo usermod -a -G www-data ftp.user_name
    www-data: is group name
    ftp.user_name is username

Add new group

sudo groupadd mynewgroup

View all groups

getent group
less /etc/group

View user groups of user

$groups ftp.user_name

Change user group

//Add an Existing User Account to a Group
usermod -a -G examplegroup username
usermod -a -G group1,group2,group3 username

// Change User's Primary group (-g)
usermod -g groupname username
usermod -g www-data ms

// Change User's Secondary group (-G)
usermod -G groupname username

Delete Groups

sudo groupdel groupname sudo delgroup {group}

Remove user from group

sudo deluser {user} {group}

Shells

cat /etc/shells
which git-shell

sudo -e 

// edit shell for user
sudo chsh <username> -s <shell name>
sudo chsh <username> -s $(which git-shell)

https://git-scm.com/book/en/v2/Git-on-the-Server-Setting-Up-the-Server

ssh

ssh -i file.pem user@host

scp

copy local files to remote
$ scp cc.zip root@host_ip:/tmp
root@host_ips's password:

scp file.txt [email protected]:/remote/directory

https://linuxize.com/post/how-to-use-scp-command-to-securely-transfer-files/

create symbolic link

ln -s source_file destination_with_name ln -s /var/www/html/uploads /home/web_uploads

Download files with curl

    download with progress displayed
        curl http://example.com --output my.file
    silent download
        curl http://example.com --output my.file --silent
    similar to above
        curl http://example.com -o my.file -s
    save filename as server
        curl -O
    follow 301 redirect
        curl -L

https://www.cyberciti.biz/faq/download-a-file-with-curl-on-linux-unix-command-line/

Postfix mail server

install at ubuntu

Run these as sudo
    $sudo apt-get update && apt-get install postfix 

    * Sending Test email
        $sudo apt-get install mailutils

Files

Setting up MTA to relay outgoing email

            /etc/postfix/main.cf
                relayhost = [smtp.gmail.com]:587
                smtp_use_tls = yes
                smtp_sasl_auth_enable = yes
                smtp_sasl_security_options =
                # @@@-DIR
                smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
                #smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt

            /etc/postfix/sasl_passwd
                [smtp.gmail.com]:587    [email protected]:password

postmap to compile and hash the contents of sasl_passwd.

Then sasl_passwd.db file will be stored in Postfix configuration directory. # @@@-DIR
$postmap /etc/postfix/sasl_passwd

Troubleshoot

$less /var/log/mail.log

Reload postfix

/etc/init.d/postfix reload
systemctl restart postfix.service

Send mail from command

// (ctrl+D) to send after enter
mail -s "Test subject" "[email protected]"

Permissions chmod

$sudo chmod 775 -R ./
    775: 7_(r1_w1_e1)_owner 7_(111)_group 5_(r1_w0_e0)_others
$sudo chmod 775 -R /var/www/somefolder

-- make script executable
$chmod u+x file.py

Permissions chown

// Make git directory owner
chown -R git:git /var/git

//created all files here to take git group
chown -R g+rws /var/git

Process

kernel statistic from userspace

~$ cat /proc/stat

Process loaded memory map

Heap, dlls/so , code linked libraries

$cat    /proc/self/maps

$cat /proc/1384/maps  
sudo cat /proc/1/maps | grep vdso
7fff39f73000-7fff39f75000 r-xp 00000000 00:00 0       [vdso]
    linux-vdso.so.1;
    libc.so.6;
    ld-linux-x86-64.so.2.

Loaded modules

 ldd /bin/uname
    linux-vdso.so.1 (0x00007ffe014b7000)
    libc.so.6 => /lib64/libc.so.6 (0x00007fbfee2fe000)
    /lib64/ld-linux-x86-64.so.2 (0x00005559aab7c000)

Tracing syscalls of process

https://www.tecmint.com/strace-commands-for-troubleshooting-and-debugging-linux/

linux trace

$ strace ls
execve("/bin/ls", ["ls"], [/* 62 vars */]) = 0

$ strace echo
execve("/bin/echo", ["echo"], [/* 62 vars */]) = 0

$ strace uname
execve("/bin/uname", ["uname"], [/* 62 vars */]) = 0

Disk and Files

view space usage of current folder

-h readable size
[root@localhost uploads]# du -h
620K    ./proof
0       ./trainees/1f
1.3M    ./trainees/2f
1.3G    ./trainees/EV
0       ./trainees/2019/12/
0       ./trainees/2019/12/

Nmap

Services running on ip nmap -T4 -A -v IP

Users

https://linuxize.com/post/how-to-list-users-in-linux/#get-a-list-of-all-users-using-the-etcpasswd-file
https://www.2daygeek.com/how-to-check-user-login-history-in-linux-using-last-lastb-lastlog-command/

View list of users

$cat /etc/passwd

View all logins

last | less
last -15

Login history of user

last | less

Wordpress

Web Applications

Web Security

Managed IT Services

Server & Network Support

Basic Linux Commands

Linux Basic commands

Information about binary

Take program to background

Bring to background

superuser and exit

login as another user without password

Copy Files, with symbolic links

File Write/Append

append

write without append

sed

Find and Replace

File Information

Readelf

Binary file (standard input) matches for non text file

Process a binary file as if it were text

Grep with lines begin with GET and sort

Since 1.3.0rc1 it's also possible to use the following:

Ec2 hosting

Open port on ec2 network setting

Creating ProFTPD Users

Troubleshoot

User and Groups

User List

Add new user

Delete User

change password of user

set user home directory

Add user to new group

Add new group

View all groups

View user groups of user

Change user group

Delete Groups

Remove user from group

Shells

ssh

scp

create symbolic link

Download files with curl

Postfix mail server

install at ubuntu

Files

Setting up MTA to relay outgoing email

postmap to compile and hash the contents of sasl_passwd.

Troubleshoot

Reload postfix

Send mail from command

Permissions chmod

Permissions chown

Process

kernel statistic from userspace

Process loaded memory map

Loaded modules

Tracing syscalls of process

linux trace

Disk and Files

view space usage of current folder

Nmap

Users

View list of users

View all logins

Login history of user