The Linux ssh server never disconnects ssh session from server side by default, check switch/router/firewall configuration to avoid the issue without changing the configuration of ssh servers/clients. If the ssh session is getting disconnected due to inactivity and one wants to stop this then please follow the below steps either on client or server side as described below: Client Side Settings To enable the keep alive system-wide (root access required), edit the configuration file … [Read more...] about How to Stop SSH Session From Getting Timed Out
This post will provide details on TCP connections reporting 'CLOSE_WAIT' states. The possible state values for TCP sockets are as follows: BOUND Bound, ready to connect or listen. CLOSED Closed. The socket is not being used. CLOSING Closed, then remote shutdown; awaiting acknowledgment. CLOSE_WAIT Remote shutdown; waiting for the socket to close. ESTABLISHED Connection has been established. FIN_WAIT_1 Socket closed; shutting down connection. … [Read more...] about Why Does “netstat” Output Show Many Connections in CLOSE_WAIT Status?
The Problem Sometimes Linux kernel logs warning messages as followings: Mar 7 09:17:14 hostname kernel: TCP: Possible SYN flooding on port 26450. Sending cookies. or Mar 7 09:17:14 hostname kernel: TCP: Possible SYN flooding on port 26450. Dropping request. The Solution This is a warning message, which indicates that the server is frequently attempted to connect to the specific port, and the kernel warns that this might possibly be an SYN flood attack(=DoS(Denial of Service) … [Read more...] about Kernel Logs Warning Messages “kernel: Possible SYN flooding on port X. Sending cookies” is logged”
There are entries in the /var/log/messages file as shown below: # tailf /var/log/messages Aug 22 11:08:21 server kernel: martian source 192.168.12.197 from 192.168.12.198, on dev eth0 Aug 22 11:08:21 server kernel: ll header: 08:00:00:00:45:00:01:00:00:00:40:00:40:11:9f:11:c0:a8:0c:c6:c0:a8:0c:c5 Aug 22 11:08:22 server kernel: martian source 192.168.12.192 from 192.168.12.198, on dev eth0 Aug 22 11:08:22 server kernel: ll header: … [Read more...] about Why Does “/var/log/messages” Report Martian Packets
What is Fiber Channel HBA Queue Depth The queue depth indicates the number of I/O requests that are "in flight", that have been requested but not yet been acknowledged to have been completed when communicating with a SAN storage. These requests can be configured per single Logical Unit Number (LUN) that is accessed or based on the HBA. The maximum queue depth describes the value of requests which is allowed to be in flight at maximum. The maximum queue depth setting can significantly influence … [Read more...] about What is HBA Queue Depth and How to Check the Current Queue Depth Value and how to Change it
The Problem iscsiadm discovery times out when both the interfaces are up, but it works fine with single interface up. # iscsiadm -m discovery -t st -p x.x.x.x iscsiadm: connect to x.x.x.x timed out iscsiadm: connect to x.x.x.x timed out The Solution This issue could occur when two or more Ethernet interfaces are connected to the same subnet or when iSCSI connection is configured to use any specific interface. In such cases when packets are delivered to the wrong interface then the OS … [Read more...] about “iscsiadm” Discovery TimeOut With Two Or More Network Interfaces in CentOS/RHEL