Install nmap and check which ports are open.Centos 7

yum install nmap

now scan the ports with :

nmap -sT -O localhost

result:

Nmap scan report for localhost (127.0.0.1)

Host is up (0.000083s latency).

rDNS record for 127.0.0.1: localhost.localdomain

Not shown: 972 closed ports

PORT      STATE SERVICE

21/tcp    open  ftp

22/tcp    open  ssh

25/tcp    open  smtp

53/tcp    open  domain

80/tcp    open  http

110/tcp   open  pop3

111/tcp   open  rpcbind

143/tcp   open  imap

443/tcp   open  https

783/tcp   open  spamassassin

993/tcp   open  imaps

995/tcp   open  pop3s

1080/tcp  open  socks

1081/tcp  open  pvuniwien

2005/tcp  open  deslogin

2009/tcp  open  news

3005/tcp  open  deslogin

3306/tcp  open  mysql

5432/tcp  open  postgresql

8009/tcp  open  ajp13

8080/tcp  open  http-proxy

8081/tcp  open  blackice-icecap

9009/tcp  open  pichat

9080/tcp  open  glrpc

9090/tcp  open  zeus-admin

9100/tcp  open  jetdirect

10024/tcp open  unknown

10025/tcp open  unknown

No exact OS matches for host (If you know what OS is running on it, see http://nmap.org/submit/ ).

TCP/IP fingerprint:

OS:SCAN(V=6.40%E=4%D=7/23%OT=21%CT=1%CU=41542%PV=N%DS=0%DC=L%G=Y%TM=59744F1

OS:C%P=x86_64-redhat-linux-gnu)SEQ(SP=101%GCD=1%ISR=105%TI=Z%TS=A)SEQ(SP=10

OS:1%GCD=1%ISR=106%TI=Z%II=I%TS=A)OPS(O1=MFFD7ST11NW7%O2=MFFD7ST11NW7%O3=MF

OS:FD7NNT11NW7%O4=MFFD7ST11NW7%O5=MFFD7ST11NW7%O6=MFFD7ST11)WIN(W1=AAAA%W2=

OS:AAAA%W3=AAAA%W4=AAAA%W5=AAAA%W6=AAAA)ECN(R=Y%DF=Y%T=40%W=AAAA%O=MFFD7NNS

OS:NW7%CC=Y%Q=)T1(R=Y%DF=Y%T=40%S=O%A=S+%F=AS%RD=0%Q=)T2(R=N)T3(R=N)T4(R=Y%

OS:DF=Y%T=40%W=0%S=A%A=Z%F=R%O=%RD=0%Q=)T5(R=Y%DF=Y%T=40%W=0%S=Z%A=S+%F=AR%

OS:O=%RD=0%Q=)T6(R=N)T7(R=Y%DF=Y%T=40%W=0%S=Z%A=S+%F=AR%O=%RD=0%Q=)U1(R=Y%D

OS:F=N%T=40%IPL=164%UN=0%RIPL=G%RID=G%RIPCK=G%RUCK=G%RUD=G)IE(R=Y%DFI=N%T=4

OS:0%CD=S)

Network Distance: 0 hops

OS detection performed. Please report any incorrect results at http://nmap.org/submit/ .

Nmap done: 1 IP address (1 host up) scanned in 12.22 seconds

now scan from external :

nmap -sT -O <ip>

result

Starting Nmap 7.50 ( https://nmap.org ) at 2017-07-23 09:30 CEST

Nmap scan report for web.site (<ip>)

Host is up (0.035s latency).

rDNS record for <ip>: mail. web.site

Not shown: 978 closed ports

PORT     STATE    SERVICE

21/tcp   open     ftp

22/tcp   open     ssh

25/tcp   open     smtp

53/tcp   open     domain

80/tcp   open     http

110/tcp  open     pop3

111/tcp  open     rpcbind

135/tcp  filtered msrpc

139/tcp  filtered netbios-ssn

143/tcp  open     imap

443/tcp  open     https

445/tcp  filtered microsoft-ds

993/tcp  open     imaps

995/tcp  open     pop3s

1080/tcp open     socks

1081/tcp open     pvuniwien

2009/tcp open     news

3306/tcp filtered mysql

8009/tcp open     ajp13

8081/tcp open     blackice-icecap

9009/tcp open     pichat

9080/tcp open     glrpc

Device type: general purpose|media device|WAP|storage-misc

Running (JUST GUESSING): Linux 3.X|4.X|2.6.X (89%), Asus embedded (86%), Synology DiskStation Manager 5.X (86%)

OS CPE: cpe:/o:linux:linux_kernel:3 cpe:/o:linux:linux_kernel:4 cpe:/o:linux:linux_kernel:3.x cpe:/h:asus:rt-n56u cpe:/o:linux:linux_kernel:3.4 cpe:/o:linux:linux_kernel:3.10 cpe:/a:synology:diskstation_manager:5.2 cpe:/o:linux:linux_kernel:2.6.32

Aggressive OS guesses: Linux 3.2 – 4.8 (89%), Linux 3.18 (88%), Linux 3.16 (87%), Linux 3.13 or 4.2 (87%), XBMCbuntu Frodo v12.2 (Linux 3.X) (87%), ASUS RT-N56U WAP (Linux 3.4) (86%), Linux 3.13 (86%), Linux 3.12 (86%), Linux 3.8 – 3.11 (86%), Linux 4.10 (86%)

No exact OS matches for host (test conditions non-ideal).

Network Distance: 6 hops

OS detection performed. Please report any incorrect results at https://nmap.org/submit/ .

Nmap done: 1 IP address (1 host up) scanned in 15.47 seconds

 

check now for LISTENING port:

Next, check for information about the port using netstat or lsof. To check for port 834 using netstat, use the following command:

netstat -anp | grep 834

result :

tcp        0      0 127.0.0.1:9168          127.0.0.1:47834         TIME_WAIT                      

unix  2      [ ACC ]     STREAM     LISTENING     397083455 343/amavisd (ch1-av  /var/spool/amavisd/amavisd.sock

unix  2      [ ]         STREAM     CONNECTED     481728342 25062/ruby           

unix  3      [ ]         STREAM     CONNECTED     407881834 4920/dovecot         

unix  2      [ ]         STREAM     CONNECTED     481808349 25062/ruby   

The lsof command reveals similar information since it is also capable of linking open ports to services:

lsof -i | grep 834

To check if the port is associated with the official list of known services, type:

cat /etc/services

 

to check the users log in use command : who

Linux Centos 7 – Startup Services – Functions

systemctl disable httpd
Running systemctl disable removes the symlink to the service in /etc/systemd/system/*

systemctl status httpd

systemctl list-unit-files

systemctl start application.service

systemctl list-units –type=service
systemctl list-units –all –state=inactive

systemctl mask nginx.service
systemctl unmask nginx.service

systemctl edit nginx.service

To remove any additions you have made, either delete the unit’s .d configuration directory or the modified service file from /etc/systemd/system. For instance, to remove a snippet, we could type:

sudo rm -r /etc/systemd/system/nginx.service.d
To remove a full modified unit file, we would type:

sudo rm /etc/systemd/system/nginx.service
After deleting the file or directory, you should reload the systemd process so that it no longer attempts to reference these files and reverts back to using the system copies. You can do this by typing:

sudo systemctl daemon-reload

very usefull
https://www.digitalocean.com/community/tutorials/how-to-use-systemctl-to-manage-systemd-services-and-units