Server Troubleshooting

                                                                   Few daily important command 

                                                               ===============================

     1)  cal                                  --->    Display calendar for current month
     2) date                                --->    Display system date and time
     3) date -s '<value>'             --->    Change system date and time in mm/dd/yy
     4) hwclock                           --->    Display the hardware clock
     5) hwclock --hctosys           --->    Set the system time from the hardware clock
     6) clear                               --->    Clear the screen
     7) ls                                    --->    List content
     8) ls -lh                               --->    List content in long listing format
     9) cd <directory>                --->    Change directory to.
   10) cd <directory>                --->    Change directory to...
   11) cd ..                                --->   Change to parent directory
   12) cd -                                 --->   Change to previous directory
   13) cd                                   --->   Change to home directory
   14) pwd                                --->    Print work (current) directory
   15) pwd -P                           --->    Print parent working dir of this symlink dir
   16) mkdir <directory>           --->   Make directory
   17) mkdir -p <directory>      --->    Make parent directories also if it does not exist
   18) uptime                           --->    Display for how long the system has been running
   19) users                             --->    Display no. of users currently logged in
   20) whoami                         --->     Display username of current user
   21) who                               --->    Display users logged in the system with their respective terminals and time since logged in
   22) who am i                       --->    Display current user, terminal and uptime
   23) w                                   --->    Display is details which files are open on which    terminal
  24) exit                                 --->    Exit from console
  25)  init 6 /reboot                  --->    Reboot the system
  26) init 0 / halt / poweroff     --->    Halt the system after shutdown
  27) top                                 --->    To check the load , I/O and uptime 

 28) tm | grep <tracking word> -->   To track word in the on going mail log   

 29) telnet <server IP> 25       --->   To check the connectivity on SMTP port 25 , we must see some Banner like "ESMTP ESMTP"  

 30) telnet <server IP> 110     --->   To check the connectivity on POP3 port 110

 31)  telnet <server IP> 143    --->   To check the connectivity on IMAP port 143 ,                                                                 

                                                How to check the Hard-disk Space. 

                                       ======================================

"df -khT" is command to check the Had-disk space

[root@jayesh ~]# df -khT 
Filesystem    Type    Size  Used Avail Use% Mounted on
/dev/sda3     ext3    3.0G  1.2G  1.6G  43% /
/dev/sda2     ext3    4.3G  581M  3.5G  15% /var
/dev/sda1     ext3    190M   12M  169M   7% /boot
tmpfs        tmpfs    282M     0  282M   0% /dev/shm

                                                                           How to check IP of Email server 

                                                                    =====================================

"ipconfig" is command by which we can check the all IP of mail server.

[root@jayesh ~]# ifconfig 
eth0   Link encap:Ethernet  HWaddr 00:0C:29:41:E3:AB  
          inet addr:192.168.30.223  Bcast:192.168.255.255  Mask:255.255.0.0
          inet6 addr: fe80::20c:29ff:fe41:e3ab/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:831850 errors:0 dropped:0 overruns:0 frame:0
          TX packets:28820 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:104188780 (99.3 MiB)  TX bytes:2937909 (2.8 MiB)
          Interrupt:177 Base address:0x1400

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:5620 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5620 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:410473 (400.8 KiB)  TX bytes:410473 (400.8 KiB)

Now here in above example we have only one IP for eth0 , if we have multiple ethernet cards with IP then we can check individual by following command

[root@jayesh ~]# ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:0C:29:41:E3:AB  
          inet addr:192.168.30.223  Bcast:192.168.255.255  Mask:255.255.0.0
          inet6 addr: fe80::20c:29ff:fe41:e3ab/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:843223 errors:0 dropped:0 overruns:0 frame:0
          TX packets:28882 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:105207150 (100.3 MiB)  TX bytes:2944836 (2.8 MiB)
          Interrupt:177 Base address:0x1400

If you have another ethernet card  say example eth1 , then we can check by either of the below command.

[root@jayesh ~]# ifconfig eth1. 

To see all ethernet cards give below command.

[root@jayesh ~]# ifconfig | less

To come back to command prompt again type "q" to

                                                                     How to see Gateway of the server 

                                                            =======================================

"route -n" is the command by which we can see the server Gate IP.

Example :--

[root@jayesh ~]# route -n 
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth0
192.168.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth0
0.0.0.0         192.168.2.234   0.0.0.0         UG    0      0        0 eth0

Now here "192.168.2.234" is the Gateway IP of server.

                                              How to delete the gateway temporary from command line 

                                 ============================================================

"route del default" is command to delete the gateway.

Example :--

[root@jayesh ~]# route -n 
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth0
192.168.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth0
0.0.0.0         192.168.2.234   0.0.0.0         UG    0      0        0 eth0

[root@jayesh ~]# route del default 

[root@jayesh ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth0
192.168.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth0

                                                        How to re-add / newly add Gateway IP  by command line

                                             =========================================================

route add default gw <IP address> dev <ethernet card> is command to add / configure the gatway.

Example :--

[root@jayesh ~]# route -n 
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth0
192.168.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth0

[root@jayesh ~]# route add default gw 192.168.2.234 dev eth0 

[root@jayesh ~]# route -n 
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth0
192.168.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth0
0.0.0.0         192.168.2.234   0.0.0.0         UG    0      0        0 eth0

                                                          How to check ethernet link is UP or not 

                                             ================================================

"ethtool" is the command by which we can check ethernet card' attributes / option and Link status

Example :--

[root@jayesh ~]# ethtool eth0
Settings for eth0:
    Supported ports: [ TP MII ]
    Supported link modes:   10baseT/Half 10baseT/Full
                            100baseT/Half 100baseT/Full
                            1000baseT/Half 1000baseT/Full
    Supports auto-negotiation: Yes
    Advertised link modes:  10baseT/Half 10baseT/Full
                            100baseT/Half 100baseT/Full
                            1000baseT/Half 1000baseT/Full
    Advertised pause frame use: No
    Advertised auto-negotiation: Yes
    Link partner advertised link modes:  10baseT/Half 10baseT/Full
                                         100baseT/Half 100baseT/Full
    Link partner advertised pause frame use: No
    Link partner advertised auto-negotiation: Yes
    Speed: 100Mb/s
    Duplex: Full
    Port: MII
    PHYAD: 0
    Transceiver: internal
    Auto-negotiation: on
    Supports Wake-on: pumbg
    Wake-on: g
    Current message level: 0x00000033 (51)
                   drv probe ifdown ifup
    Link detected: yes

The Link "detected:yes" means , the patch cord is connected to Switch / HUB / Router.

The Link "detected:no" means , the patch cord is not connected to Switch / HUB / Router.

                                                              How to check the Mail queue of the Email server. 

                                                      ===============================================

"mailq" and "nmqt" is the command to see the email queue.

[root@jayesh ~]# mailq
-Queue ID- -----Size-- ----Arrival Time---- -Sender/Recipient-------

1904427C014    25472 Sat Oct  6 07:57:36  sender1@netcore.co.in
        (connect to lfvsfcp10127.dn.net[130.94.69.225]:25: Connection refused)
                                         recipient@lfvsfcp10127.dn.net

A28D9374004     2728 Sat Oct  6 14:49:43  sender2@netcore.co.in
(connect to p3nlhg941.shr.prod.phx3.secureserver.net[50.63.197.30]:25: Connection timed out)
                                         recipient2@p3nlhg941.shr.prod.phx3.secureserver.net

F397C1274049     2067 Sat Oct  6 15:41:54  sender3@netcore.co.in
2 http://support.google.com/mail/bin/answer.py?answer=6558 nu6si871202icb.104 (in reply to RCPT TO command))
                                         recipient@mfactorfireworks.com

-- 36831 Kbytes in 3 Requests.

OR

[root@nlb2 ~]# nmqt 
3

The above command means on server "3" emails are in queue.

                                                                How to check the Internet OR LAN connectivity. 

                                                        ==================================================

"ping" is the command by which we can check the internet connectivity.

Example :--    ping -c 3 <ip / host name>

LAN IP ping check

[jayesh@jayesh ~]$ ping 192.168.2.234 -c 3 
PING 192.168.2.234 (192.168.2.234) 56(84) bytes of data.
64 bytes from 192.168.2.234: icmp_req=1 ttl=64 time=0.315 ms
64 bytes from 192.168.2.234: icmp_req=2 ttl=64 time=0.384 ms
64 bytes from 192.168.2.234: icmp_req=3 ttl=64 time=0.312 ms

--- 192.168.2.234 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 1999ms
rtt min/avg/max/mdev = 0.312/0.337/0.384/0.033 ms

Internet IP ping check

[root@jayesh ~]# ping yahoo.com -c 3 
PING yahoo.com (98.138.253.109) 56(84) bytes of data.
64 bytes from ir1.fp.vip.ne1.yahoo.com (98.138.253.109): icmp_seq=1 ttl=45 time=369 ms
64 bytes from ir1.fp.vip.ne1.yahoo.com (98.138.253.109): icmp_seq=2 ttl=46 time=292 ms
64 bytes from ir1.fp.vip.ne1.yahoo.com (98.138.253.109): icmp_seq=3 ttl=46 time=377 ms

--- yahoo.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2000ms
rtt min/avg/max/mdev = 292.231/346.275/377.582/38.381 ms

                                                                                           How to check Load 

                                                                               ==============================

Observing the output of things like  top , uptime,   w  and perhaps others, you certainly pay for the line  load average  

Try to understand the meaning of these numbers.   So, in other words, the numbers reflect the number of blocking processes in the queue for execution at a specific time interval, namely, 1 minute, 5 minutes and 15 minutes, respectively.  In this case, the blocking process - a process that is waiting for resources to continue.   As a rule, there is the expectation of resources such as CPU, disk I / O or network I / O subsystem.

High values of   load average load average indicate that the system can not cope with the load. . When it comes to the target server that is under heavy load, it is usually helpful to fine-tune the operating system (the network subsystem, the restriction on the number of open files, and so on).  High CPU can also be caused by hardware problems, such as failure of the drive.

For the diagnosis of appeal to other useful data provided output   top . Line CPU (s)   contains information on the distribution of CPU time.The first two values directly reflect the work of CPU processing processes:

Prolonged high (99-100%) indicators point to the CPU as a bottleneck.

   Parameter wa  suggests a simple, connected to I / O:

Above 80% is considered normal and not quite clearly shows us that the processor spends a lot of time waiting for I / O (this usually means that the failure of HDD or NIC).

SAR command :-- 

We can Also check the Load and I/O with SAR command , The SAR command come with sysstat-7.0.2-1.el5.rpm package. Which need to be install.

Example :--   sar <-switch> <time interval in sec> <number of time o/p require>

For checking the i/owait of server give . "-u" switch use for checking the "iowait"

[root@jayesh ~]# sar -u 2 5
Linux 2.6.18-92.el5 (Jayesh)     10/10/2012

05:30:57 PM       CPU     %user     %nice   %system   %iowait    %steal     %idle
05:30:59 PM       all         75.08      0.00       21.45          0.33       0.66         2.48
05:31:01 PM       all         72.55      0.00       20.75          0.82      0.49          5.39
05:31:03 PM       all         72.33      0.00       21.67          2.33      0.67          3.00
05:31:05 PM       all         75.99      0.00       13.74          0.17      1.16          8.94
05:31:07 PM       all         74.63      0.00       17.18          0.82      1.15         6.22
Average:          all           74.12      0.00       18.96          0.89      0.82         5.21

For checking the Server Load  give . "-q" switch

[root@jayesh ~]# sar -q 2 5
Linux 2.6.18-92.el (jayesh)     10/10/2012

05:35:05 PM   runq-sz  plist-sz   ldavg-1   ldavg-5  ldavg-15
05:35:07 PM         5       246         11.18     11.63     12.03
05:35:09 PM         5       245        11.18     11.63     12.03
05:35:11 PM         9       245        11.09     11.60     12.02
05:35:13 PM         8       245       11.09     11.60     12.02
05:35:15 PM         6       245       11.09     11.60     12.02
Average:             7       245       11.13     11.61     12.02
                               

                                                        How to check connectivity by telnet 

                                                 ===============================

For checking the connectivity from Windows desktop , Go to  Start ---> Run ---> cmd  and then execute the below commands.

Checking the connectivity on POP3 ( 110 port )

[root@jayesh ~]# telnet pop2.netcore.co.in 110
Trying 202.162.229.40...
Connected to pop2.netcore.co.in (202.162.229.40).
Escape character is '^]'.
+OK pop2.netcore.co.in Cyrus POP3 v2.4.12-Invoca-RPM-2.4.12-2 server ready <11008234458491230169.1349936105@pop2.netcore.co.in>

Checking the connectivity on IMAP ( 143 port )

[root@jayesh ~]# telnet pop2.netcore.co.in 143
Trying 202.162.229.40...
Connected to pop2.netcore.co.in (202.162.229.40).
Escape character is '^]'.
* OK [CAPABILITY IMAP4rev1 LITERAL+ ID ENABLE STARTTLS AUTH=PLAIN SASL-IR] pop2.netcore.co.in Cyrus IMAP v2.4.12-Invoca-RPM-2.4.12-2 server ready

Checking the connectivity on SMTP ( port 25 )

[root@jayesh ~]# telnet  smtp3.netcore.co.in  25
Trying 202.162.240.180...
Connected to smtp3.netcore.co.in (202.162.240.180).
Escape character is '^]'.
220 ESMTP ESMTP

                                                                  How to check whether Email id and password is correct 

                                                        =========================================================

For checking whether Email ID and passwords are correct from Windows desktop , Go to  Start ---> Run ---> cmd  and then execute the below commands.  Enter the authenticated ID and authenticate password which you use in Outlook or in Webmail.  If  we are not getting output mention in blue , then either your email id or password is incorrect.

[root@jayesh ~]# telnet pop2.netcore.co.in 143
Trying 202.162.229.40...
Connected to pop2.netcore.co.in ( 202.162.229.40).
Escape character is '^]'.
* OK [CAPABILITY IMAP4rev1 LITERAL+ ID ENABLE STARTTLS AUTH=PLAIN SASL-IR] tower.netcore.co.in Cyrus IMAP v2.4.12-Invoca-RPM-2.4.12-2 server ready
a login jayesh.shinde@netcore.co.in password123
a OK [CAPABILITY IMAP4rev1 LITERAL+ ID ENABLE ACL RIGHTS=kxte QUOTA MAILBOX-REFERRALS NAMESPACE UIDPLUS NO_ATOMIC_RENAME UNSELECT CHILDREN MULTIAPPEND BINARY CATENATE CONDSTORE ESEARCH SORT SORT=MODSEQ SORT=DISPLAY THREAD=ORDEREDSUBJECT THREAD=REFERENCES ANNOTATEMORE LIST-EXTENDED WITHIN QRESYNC SCAN XLIST URLAUTH URLAUTH=BINARY X-NETSCAPE LOGINDISABLED COMPRESS=DEFLATE IDLE] User logged in SESSIONID=<pop2.netcore.co.in-8649-1349952658-1>
^]
telnet> q
Connection closed.

[root@jayesh ~]# telnet 202.162.229.40 110 
Trying 202.162.229.40
Connected to port2.netcore.co.in (202.162.229.40).
Escape character is '^]'.
+OK pop2.netcore.co.in Cyrus POP3 v2.4.12-Invoca-RPM-2.4.12-2 server ready <12775447681623682887.1349952689@pop2.netcore.co.in>
user jayesh.shinde@netcore.co.in
+OK Name is a valid mailbox
pass password123
+OK Mailbox locked and ready SESSIONID=<pop2.netcore.co.in-12165-1349952689-1>
^]
telnet> q
Connection closed.

                                                                  How to send email by telnet  + SMTP Auth 

                                                      ======================================== 

Telnet from your computer to the mail server.
     $ telnet 192.168.30.223 25
 You should receive a reply like:
    Trying 192.168.30.223...
      Connected to 192.168.30.223 (192.168.30.223).
      Escape character is '^]'.
      220 ESMTP ESMTP

 If the last line is made of lots of stars with an occasional 2 or 0 then you are probably going through a Cisco PIX, and none of the extended commands will work.

You will then need to declare where you are sending the email from. You can use either standard or extended SMTP commands to do this. Extended commands allow you to see what is supported by the server and to authorize yourself:

Dont worry too much about your local domain name although you really should use your exact fully qualified domain name as seen by the outside world the mail server has no choice but to take your word for it as of RFC822-RFC1123.

Now give your email address:
     MAIL FROM: <jayesh.shinde@netcore.co.in>
 The angle brackets around the name are important; some servers won't accept the name unless they are there.
 Should yield:
     250 2.1.0 jayesh.shinde@netcore.co.in... Sender ok

Now give the recipients address:
     RCPT TO: <netcoresolutions@gmail.com>
 Again, use the angle brackets.
 Should yield:
     250 2.1.0 netcoresolutions@gmail.com... Recipient ok

To start composing the message issue the command:
      DATA
     Subject:-test mail 1- 
 then press enter twice (these are needed to conform to RFC 882)
 You may now proceed to type the body of your message on as many lines as it takes. To tell the mail server that you have completed the message enter a single "." on a line by itself.
 The mail server should reply with:
     250 2.0.0 ???????? Message accepted for delivery

You close the connection by issuing:
     QUIT
 The mailserver should reply with something like:
      221 2.0.0 192.168.30.223 closing connection
     Connection closed by foreign host. 

Summary :--

     telnet 192.168.30.223 25
      Trying 192.168.30.223...
      Connected to 192.168.30.223 (192.168.30.223).
      Escape character is '^]'.
      220 ESMTP ESMTP
      EHLO netcore.co.in
      250-location.exampledomain.com
      250-PIPELINING
      250-SIZE 9999360
      250-VRFY
      250-ETRN
      250-AUTH LOGIN PLAIN
      250-AUTH=LOGIN PLAIN
      250-ENHANCEDSTATUSCODES
      250-8BITMIME
      250 DSN
      AUTH LOGIN
      334 amF5ZXNoLnNoaW5kZUBuZXRjb3JlLmNvLmlu
      bmFtZQ==
      334 cGFzc3dvcmQxMjM=
      U2VjcmV0
      235 2.0.0 OK Authenticated
      MAIL FROM: <jayesh.shinde@netcore.co.in>
      250 2.1.0 jayesh.shinde@netcore.co.in... Sender ok
      RCPT TO: <netcoresolutions@gmail.com>
      250 2.1.0 netcoresolutions@gmail.com... Recipient ok
      DATA
      Subject:- Test email 1
      Welcome to netCORE
      .
     250 2.0.0 ???????? Message accepted for delivery
     QUIT
     221 2.0.0 192.168.30.223 closing connection
     Connection closed by foreign host.