Details about NFS timeout on Red Hat Enterprise Linux 5

There are two mount options for timeouts of an NFS request.

# timeo: a timeout value. the unit is 1/10 seconds.
# retrans: a retrans count.

An NFS client waits an RPC response for timeo before issuing an RPC request. If the request is timed out, the NFS client retransmits the request and waits a response again for tomeo*2. The timeout valueis doubled until it reachs a maximum value. The maximum timeout is timeo*(retrans+1) in TCP, is NFS_MAX_UDP_TIMEOUT in UDP. The RPC timeout is called minor timeout. If the timeout reaches maximum timeout, the NFS request is timeout. That timeout is called major timeout. The default value of timeo is 60 seconds in TCP, is 1.1 seconds in UDP, and the default value of retrans is 2 in both of TCP/UDP. The maximum value of timeo is NFS_MAX_TCP_TIMEOUT in TCP, is NFS_MAX_UDP_TIMEOUT in UDP, and NFS_MAX_TCP_TIMEOUT is 600 seconds, and NFS_MAX_UDP_TIMEOUT is 60 seconds.

Capture packets using tcpdump to troubleshoot NFS issue. Like :

#tcpdump -vv -s 0 -i ethX -w /tmp/printdump_server.cap host {hostname or IP address of client/server}

Replace ethX, and IP of server/client. Packets must be captured at the same time on client and nfs server. Then analysis it using wireshark.

Try :)

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How to check or read email with telnet

Do following :

#telnet example.com 110
#user username@example.com
#pass yourpasswordgoeshere
#list
#retr id
#dele id

quit

Done

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How to check or read email with telnet

Do following :

#telnet example.com 25
#ehlo example.com
#mail from: username@example.com
#rcpt to: friend@hotmail.com, friend2@yahoo.com
#data
Subject: My Telnet Test Email

Hello,

This is an email sent by using the telnet command.

Your friend,
Me

.

done

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How linux calls happens while it starts ?

We start the Linux kernel first from C code executed from ''startup_32:'' asm label:

|startup_32:
|start_kernel
|lock_kernel
|trap_init
|init_IRQ
|sched_init
|softirq_init
|time_init
|console_init
|#ifdef CONFIG_MODULES
|init_modules
|#endif
|kmem_cache_init
|sti
|calibrate_delay
|mem_init
|kmem_cache_sizes_init
|pgtable_cache_init
|fork_init
|proc_caches_init
|vfs_caches_init
|buffer_init
|page_cache_init
|signals_init
|#ifdef CONFIG_PROC_FS
|proc_root_init
|#endif
|#if defined(CONFIG_SYSVIPC)
|ipc_init
|#endif
|check_bugs
|smp_init
|rest_init
|kernel_thread
|unlock_kernel
|cpu_idle

* startup_32 [arch/i386/kernel/head.S]
* start_kernel [init/main.c]
* lock_kernel [include/asm/smplock.h]
* trap_init [arch/i386/kernel/traps.c]
* init_IRQ [arch/i386/kernel/i8259.c]
* sched_init [kernel/sched.c]
* softirq_init [kernel/softirq.c]
* time_init [arch/i386/kernel/time.c]
* console_init [drivers/char/tty_io.c]
* init_modules [kernel/module.c]
* kmem_cache_init [mm/slab.c]
* sti [include/asm/system.h]
* calibrate_delay [init/main.c]
* mem_init [arch/i386/mm/init.c]
* kmem_cache_sizes_init [mm/slab.c]
* pgtable_cache_init [arch/i386/mm/init.c]
* fork_init [kernel/fork.c]
* proc_caches_init
* vfs_caches_init [fs/dcache.c]
* buffer_init [fs/buffer.c]
* page_cache_init [mm/filemap.c]
* signals_init [kernel/signal.c]
* proc_root_init [fs/proc/root.c]
* ipc_init [ipc/util.c]
* check_bugs [include/asm/bugs.h]
* smp_init [init/main.c]
* rest_init
* kernel_thread [arch/i386/kernel/process.c]
* unlock_kernel [include/asm/smplock.h]
* cpu_idle [arch/i386/kernel/process.c]

The last function ''rest_init'' does the following:

1. launches the kernel thread ''init''
2. calls unlock_kernel
3. makes the kernel run cpu_idle routine, that will be the idle loop executing when nothing is scheduled

In fact the start_kernel procedure never ends. It will execute cpu_idle routine endlessly.

Follows ''init'' description, which is the first Kernel Thread:

|init
|lock_kernel
|do_basic_setup
|mtrr_init
|sysctl_init
|pci_init
|sock_init
|start_context_thread
|do_init_calls
|(*call())-> kswapd_init
|prepare_namespace
|free_initmem
|unlock_kernel
|execve
=========

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How to use ethtool ?

#ethtool -g|--show-ring eth0
#ethtool -A ethX [autoneg on|off] [rx on|off] [tx on|off]
#ethtool -c|--show-coalesce ethX
#ethtool -C|--coalesce ethX //change coalesce values

To avoid flooding the host system with too many interrupts, packets are collected and one single interrupt is generated for multiple packets. This is called interrupt coalescing.

#ethtool -G|--set-ring ethX [rx N] [rx-mini N] [rx-jumbo N] [tx N]
#ethtool -i|--driver ethX
#ethtool -k|--show-offload ethX
#ethtool -K|--offload ethX [rx on|off] [tx on|off] [sg on|off] [tso on|off] [ufo on|off] [gso on|off] [gro on|off] [lro on|off]
#ethtool -S|--statistics ethX //Queries the specified ethernet device for NIC- and driver-specific statistics.
#ethtool -t|--test ethX [offline|online]
#ethtool -s ethX speed N [duplex half|full] [port tp|aui|bnc|mii] [autoneg on|off] [advertise N] [phyad N] [xcvr inter-
nal|external] [wol p|u|m|b|a|g|s|d...] [sopass xx:yy:zz:aa:bb:cc] [msglvl N]

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How to make bridge over VLAN?

How to make bridge over VLAN?

Bridging over VLAN's :

By constructing a bridge between a "normal" and a "VLAN" ethernet interface, the Linux computer will add and remove the VLAN headers on behalf of any other device(s) plugged into the "normal" card.

How :

Okay, now for the tricky part. It takes a slight modification of the procedures above. For this example, let's presume we have an Ethernet interface eth0 connected to the network where a VLAN id 2 is present, and we have a device or devices on eth1 that need to be bridged into that VLAN 2.

Go ahead and first construct the VLAN interface like we did before (copy ifcfg-eth#, change DEVICE, add VLAN=yes), except also remove the BOOTPROTO, IPADDR, NETMASK, and GATEWAY lines if present. Add a line BRIDGE=br2 (or a different named bridge device of your choice).

1. vi /etc/sysconfig/network-scripts/ifcfg-eth0.2 (connected to VLAN2)

---
DEVICE=eth0.2
VLAN=yes
TYPE=Ethernet
HWADDR=##:##:##:##:##:##
ONBOOT=yes
BRIDGE=br2
----

2. vi /etc/sysconfig/network-scripts/ifcfg-eth1

--
DEVICE=eth1
TYPE=Ethernet
WADDR=##:##:##:##:##:##
ONBOOT=yes
BRIDGE=br2
---

3. vi /etc/sysconfig/network-scripts/ifcfg-br2

----
DEVICE=br2
TYPE=Bridge
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.2.24
NETMASK=255.255.255.0
GATEWAY=192.168.2.254
DELAY=0
STP=off
---

Note : IP address has in br2

4. service network restart. That's it.

Try :)

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How to setup VLAN network on linux ?

How to setup VLAN network on linux ?

Why VLAN : create a virual lan(grouping some computers from actual LAN with out using any switch/routers etc. Only needs software. Can also be done using hardware)

Required Packages :

#yum install vconfig

Next, go to the /etc/sysconfig/network-scripts directory and decide which eth# device you're going to add a VLAN to. Note that the VLAN device will run alongside (in parallel to, at the same time) as the original eth# device, so there is no need to change your existing configuration.

1. copy /etc/sysconfig/network-scripts/ifcfg-eth0 to etc/sysconfig/network-scripts/ifcfg-eth0.2 and edit : VLAN=yes like :
---
DEVICE=eth0.2
VLAN=yes
TYPE=Ethernet
HWADDR=##:##:##:##:##:##
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.1.24
GATEWAY=192.168.1.254
---

Note : VLAN id is here 2 for eth0

2. Do for other nic and increase VLAN ID and check like ifconfig
3. Restart network service. That's it.

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