1. Give an example of set of shell commands that will give you the number of files in a directory
2. How do you tell what process has a TCP port open in Linux
3. On a Red Hat Linux Variant how do you control whether a service starts when the system boots
4. How do you tell the amount of free disk space left on a volume
5. Give an example of a set of shell commands to tell how many times “bob” has logged on to the system this month
6. Give an example of a recursively copying a directory from one location to another.
7. How do you modify the IP and Net mask of a system running a Red Hat Variant of Linux
8. Give an example of a set of shell commands that will give you the number of “httpd” processes running on a Linux box.
9. On CentOS or Fedora based system using the package management application, how do you tell what package provided the file “libnss_ldap.so”
10. What is the difference between VTP client, server, and transparent
11. What is the maximum length of CAT6
12. How does one set up a layer two link to share VLANs
13. How does one implement redundant links at Layer 2
14. What is the difference between a hub, switch, and a router
a. What are the security advantages of switch vs. hub
15. Show an example of using telnet to learn the headers of an http server.
16. In what OSI layer does PPP exist
17. What’s the difference between TCP and UDP
18. Given a DNS server that has just started (with an empty cache) and host contacting this DNS server (using it’s OS setting) to learn an address for google.com, list the steps the DNS server will take to learn it with IP addresses (each step will have multiple possible IP addresses – you need choose only one per step).
19. Why are layer 2 loops bad, and what protocol was designed to prevent them
20. Given a radius server at 10.0.0.2 and a shared key of ‘abc123’ show the IOS commands necessary to authenticate switch users against the radius server, while still allowing the use of local username / password pairs
Archive for the ·
UNIX Interview questions and answers
1. Give an example of set of shell commands that will give you the number of files in a directory
- What is sed? – sed is stream editor, a Unix tool for working with streams of text data. See the awful truth about sed.
- How do you substitute strings with sed? – Use ’s/old/new’ command, so sed ’s/hello/goodbye/’ would substitute the occurrence of the word hello to goodbye.
- How do you inject text with sed? – & in the substitution string defines the pattern found in the search string. As an example, here’s us trying to find a word ‘hello’ and replacing it with ‘hello and how are you’:
echo ‘hello there’ | sed ’s/^hello/& and how are you/’
- Can I find several patterns and refer to them in the replacement string? – Yes, use (pattern) and then refer to your patterns as \1, \2, \3 and so on.
- If the string is ‘old old old’ and I run ’s/old/new’, I get ‘new old old’ as the result. I need ‘new new new‘. – You forgot the global modifier, which would replace every occurrence of the pattern with the substitution. ’s/old/new/g‘ will work.
- But I want ‘old old new’ from the previous example. – Just use the numeric modifier saying you want the third occurrence to be replaced. ’s/old/new/3‘ will work.
- I wrote a rather complex sed script. How do I save and run it? – Assuming that your file is named myscript1.sed, you can invoke sed -f myscript1.sed.
- How do I delete trailing whitespaces from each line? – sed ’s/[ \t]*$//’ Here we’re replacing any occurrence of a space or a tab with nothing. Check sed one-liners for more examples.
- How do you print just a few first lines of the file? – sed 1q will give you just the first line, sed 10q the first 10 lines.
- How do you replace a pattern only if it’s found, so that it’s executed faster? – Nest the replacement statement: sed ‘/old/ s/old/new/g’ file.txt
Original Article: http://www.ugetjob.com/?p=428
I collected some useful interview questions from various sites and I thought these questions might help our readers or job seekers to strength their knowledge. Most of the questions are AIX, HACMP, Network related. Enjoy.
Can you explain the steps to Mirroring rootvg in your environment?
Mirroring “rootvg” protects the operating system from a disk failure. Mirroring “rootvg” requires a couple extra steps compared to other volume groups. The mirrored rootvg disk must be bootable *and* in the bootlist. Otherwise, if the primary disk fails, you’ll continue to run, but you won’t be able to reboot.
In brief, the procedure to mirror rootvg on hdisk0 to hdisk1 is
1. Add hdisk1 to rootvg: extendvg rootvg hdisk1
2. Mirror rootvg to hdisk1: mirrorvg rootvg hdisk1 (or smitty mirrorvg)
3. Create boot images on hdisk1: bosboot -ad /dev/hdisk1
4. Add hdisk1 to the bootlist:bootlist -m normal hdisk0 hdisk1
5. Reboot to disable quorum checking on rootvg. The mirrorvg turns off quorum by default, but the system needs to be rebooted for it to take effect.
What is VPN and how it works?
A VPN is a private network that uses a public network (usually the Internet) to connect remote sites or users together. Instead of using a dedicated, real-world connection such as leased line, a VPN uses “virtual” connections routed rough the Internet from the company’s private network to the remote site or employee.
What is daemon?
A daemon (pronounced DEE-muhn) is a program that runs continuously and exists for the purpose of handling periodic service requests that a computer system expects to receive. The daemon program forwards the requests to other programs (or processes) as appropriate. Each server of pages on the Web has an HTTPD or Hypertext Transfer Protocol daemon that continually waits for requests to come in from Web clients and their users.
There are several daemon in AIX environment, such as, sshd, inetd, and so on.
Can you describe SAN in your won word?
A storage area network (SAN) is a high-speed special-purpose network (or subnetwork) that interconnects different kinds of data storage devices with associated data servers on behalf of a larger network of users. Typically, a storage area network is part of the overall network of computing resources for an enterprise. A storage area network is usually clustered in close proximity to other computing resources such as IBM Power5 boxes but may also extend to remote locations for backup and archival storage, using wide area network carrier technologies such as ATM or SONET .
A storage area network can use existing communication technology such as IBM’s optical fiber ESCON or it may use the newer Fibre Channel technology. Some SAN system integrators liken it to the common storage bus (flow of data) in a personal computer that is shared by different kinds of storage devices such as a hard disk or a CD-ROM player.
SANs support disk mirroring, backup and restore, archival and retrieval of archived data, data migration from one storage device to another, and the sharing of data among different servers in a network. SANs can incorporate subnetworks with network-attached storage (NAS) systems.
So you mention NAS, but What is NAS?
Network-attached storage (NAS) is hard disk storage that is set up with its own network address rather than being attached to the department computer that is serving applications to a network’s workstation users. By removing storage access and its management from the department server, both application programming and files can be served faster because they are not competing for the same processor resources. The network-attached storage device is attached to a local area network (typically, an Ethernet network) and assigned an IP address. File requests are mapped by the main server to the NAS file server.
Network-attached storage consists of hard disk storage, including multi-disk RAID systems, and software for configuring and mapping file locations to the network-attached device. Network-attached storage can be a step toward and included as part of a more sophisticated storage system known as a storage area network (SAN).
NAS software can usually handle a number of network protocols, including Microsoft’s Internetwork Packet Exchange and NetBEUI, Novell’s Netware Internetwork Packet Exchange, and Sun Microsystems’ Network File System. Configuration, including the setting of user access priorities, is usually possible using a Web browser.
What is SMTP and how it works?
SMTP (Simple Mail Transfer Protocol) is a TCP/IP protocol used in sending and receiving e-mail. However, since it is limited in its ability to queue messages at the receiving end, it is usually used with one of two other protocols, POP3 or IMAP, that let the user save messages in a server mailbox and download them periodically from the server. In other words, users typically use a program that uses SMTP for sending e-mail and either POP3 or IMAP for receiving e-mail. On Unix-based systems, sendmail is the most widely-used SMTP server for e-mail. A commercial package, Sendmail, includes a POP3 server. Microsoft Exchange includes an SMTP server and can also be set up to include POP3 support.
SMTP usually is implemented to operate over Internet port 25.
Do you have any idea about NAT?
Short for Network Address Translation, an Internet standard that enables a local-area network (LAN) to use one set of IP addresses for internal traffic and a second set of addresses for external traffic. A NAT box located where the LAN meets the Internet makes all necessary IP address translations.
NAT serves three main purposes:
- Provides a type of firewall by hiding internal IP addresses
- Enables a company to use more internal IP addresses. Since they’re used internally only, there’s no possibility of conflict with IP addresses used by other companies and organizations.
- Allows a company to combine multiple ISDN connections into a single Internet connection.
Explain DHCP and its uses to an environment?
Short for Dynamic Host Configuration Protocol, a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device’s IP address can even change while it is still connected. DHCP also supports a mix of static and dynamic IP addresses.
Dynamic addressing simplifies network administration because the software keeps track of IP addresses rather than requiring an administrator to manage the task. This means that a new computer can be added to a network without the hassle of manually assigning it a unique IP address. Many ISPs use dynamic IP addressing for dial-up users.
What does SNMP stands for?
Short for Simple Network Management Protocol, a set of protocols for managing complex networks. SNMP works by sending messages, called Protocol Data Units, to different parts of a network. SNMP-compliant devices, called Agents, store data about themselves in Management Information Bases and return this data to the SNMP requesters.
What do you know about TCPDump?
TCPdump is a common computer network debugging tool that runs under the command line. It allows the user to intercept and display TCP/IP and other packets being transmitted or received over a network to which the computer is attached. Tcpdump works on most Unix-like platforms: Linux, Solaris, BSD, Mac OS X, HP-UX and AIX among others. On Windows, WinDump can be used; it’s a port of tcpdump to Windows.
You must have a root or super user authority to use TCPdumps in UNIX like envrionment.
How do I remove a volume group with no disks?
This is a very common question about AIX LVM and I knew that you will ask me this one. Within a volume group there is a Volume Group Descriptor Area (VGDA) which is kinda a “suitcase” of lvm information. This is what allows you to pick up your drives and take them to another machine, importvg them, and get filesystems automatically defined.
What happens, when you importvg the volume group, the command goes out and reads the VGDA and finds out about all the logical volumes and filesystems that may exist on the
volume group. It then checks for clashes (name conflicts, etc..) on its own machine and then, populates its own database with information about the new volume group and
its associated logical volumes. In cases of file systems, it will go into the /etc/filesystems file and add the new filesystem entries that came along with the imported volume group.
The main question I see is “I’ve taken away the disks, but how do I get rid of the volume group”. The question should really say, “How do I get rid of the volume group INFORMATION” since that’s all you have on the system. You’ve got possible entries in
the /etc/filesystems and definitely entries in the ODM. Just do:
It does a reverse importvg, except it doesn’t go off and read the VGDA. It nukes anything relating to the volume group in the /etc/filesystems and ODM. The only time this won’t work is if the system detects that the volume group is varied on. Then, it would be like trying to change tires on a moving car, we won’t let you do it!
How do you you get rid of a disk that is no longer really in the VG?
In this case, you DON’T want to do an exportvg. What you want to do is tell the system you want to cut out the memory of the old, bad disk from the RS/6000 AND from the VGDA of the volume group. You simply do: reducevg -d -f
or if the hdname can’t be found:
reducevg -d -f
Be careful with this command. Unlike the exportvg command, actions done
with this command WILL affect the VGDA information on the platter.
What is Capacity on Demand?
Capacity on Demand (CoD) encompasses the various capabilities for you to dynamically activate one or more resources on your server as your business peaks dictate. You can activate inactive processors or memory units that are already installed on your server on a temporary and permanent basis.
Usually, the Capacity on Demand is used for IBM System i5™ and eServer™ i5 and IBM System p5™ and eServer p5 520, 550, 570, 590, and 595 models. Some servers include a number of active and inactive resources. Active processors and active memory units are resources that are available for use on your server when it comes from the manufacturer. Inactive processors and inactive memory units are resources that are included with your server but are not available for use until you activate them.
What is Hardware Management Console (HMC)?
The HMC is a server or stand alone machine that provides a graphical user interface tool to manage several Power Systems. The HMC manages system through hypervisor and operating system. From version 7 it is truly web based and you can configure, installs and manage, partitioned, virtualization most of your Power5 and 6 boxes via HMC. There are many tasks you can do with HMC, such as,
- Powering off and on of the partition
- Configure and activate resources to the system
- Creates and stores LPAR profiles and allocated resources to them.
- HMC do the dynamic memory reconfiguration of the partition.
- Setup VIO server and VIO client thru HMC and do micro-partition, create storage
- pool and processor pool with it
- Provide virtual console to the partition
Most of the time we installed dual HMC for redundancy and make sure to achieve more uptime in a wide system
Why do I need a Hardware Management Console, anyway?
You need a HMC if you plan to:
– Configure and manage logical partitions and partition profiles (selected models can configure LINUX partitions without a HMC).
– Perform DLPAR (dynamic LPAR) functions.
– Activate and manage Capacity on Demand resources.
You can also use the HMC to:
– Perform service functions
– Manage frames (towers), IOPs and IOAs. * Note that you cannot see below the IOA to the device level.
– Manage system profiles (yes, you can have more than one!)
– Power on and power down. The Service Processor is always hot if there is power to the server.
– Activate and manage Virtualization Engine technologies.
– 5250 emulation so you can get a console up on a i5/OS partition or a virtual terminal window for AIX or LINUX.
What is kernel?
The kernel is the essential center of a computer operating system, the core that provides basic services for all other parts of the operating system. A synonym is nucleus. A kernel can be contrasted with a shell, the outermost part of an operating system that interacts with user commands. Kernel and shell are terms used more frequently in UNIX operating systems than in IBM mainframe or Microsoft Windows systems.
Typically, a kernel (or any comparable center of an operating system) includes an interrupt handler that handles all requests or completed I/O operations that compete for the kernel’s services, a scheduler that determines which programs share the kernel’s processing time in what order, and a supervisor that actually gives use of the computer to each process when it is scheduled. A kernel may also include a manager of the operating system’s address spaces in memory or storage, sharing these among all components and other users of the kernel’s services. A kernel’s services are requested by other parts of the operating system or by application programs through a specified set of program interfaces sometimes known as system calls.
What is RMC?
The Resource Monitoring and Control (RMC) subsystem is the scalable backbone of RSCT that provides a generalized framework for managing resources within a single system or a cluster. Its generalized framework is used by cluster management tools to monitor, query, modify, and control cluster resources. RMC provides a single monitoring and management infrastructure for both RSCT peer domains and management domains. RMC can also be used on a single machine, enabling you to monitor and manage the resources of that machine. However, when a group of machines, each running RMC, are clustered together, the RMC framework allows a process on any node to perform an operation on one or more resources on any other node in the domain.
What information is stored in Object Data Manager?
It is a database of system and device configuration information integrated into IBM’s AIX operating system. The ODM is unique to AIX compared to other UNIX operating systems.
Example of information stored in the ODM database are:
- Network configuration
- Logical volume management configuration
- Installed software information
- Devices that AIX has drivers for
- Logical devices or software drivers
- Physical hardware device installed
- Menus, screens and commands that SMIT uses
Explain a little about Vital Product Data (VPD)?
VPD in AIX and Linux is a collection of configuration and informational data associated with a particular set of hardware or software. VPD refers to a subset of database tables in the Object Data Manager (ODM), Therefore the VPD and ODM terms are sometimes referred to interchangeably.
Vital product data (VPD) stores information such as part numbers, serial numbers, and engineering change levels from the Customized VPD object class or platform specific areas, not all devices contain VPD data.
Does HACMP work on different operating systems?
Yes. HACMP is tightly integrated with the AIX 5L operating system and System p servers allowing for a rich set of features which are not available with any other combination of operating system and hardware. HACMP V5 introduces support for the Linux operating system on POWER servers. HACMP for Linux supports a subset of the features available on AIX 5L, however this mutli-platform support provides a common availability infrastructure for your entire enterprise.
What applications work with HACMP?
All popular applications work with HACMP including DB2, Oracle, SAP, WebSphere, etc. HACMP provides Smart Assist agents to let you quickly and easily configure HACMP with specific applications. HACMP includes flexible configuration parameters that let you easily set it up for just about any application there is.
Does HACMP support dynamic LPAR, CUoD, On/Off CoD, or CBU?
HACMP supports Dynamic Logical Partitioning, Capacity Upgrade on Demand, On/Off Capacity on Demand and Capacity Backup Upgrade.
If a server has LPAR capability, can two or more LPARs be configured with unique instances of HACMP running on them without incurring additional license charges?
Yes. HACMP is a server product that has one charge unit: number of processors on which HACMP will be installed or run. Regardless of how many LPARs or instances of AIX 5L that run in the server, you are charged based on the number of active processors in the server that is running HACMP. Note that HACMP configurations containing multiple LPARs within a single server may represent a potential single point-of-failure. To avoid this, it is recommended that the backup for an LPAR be an LPAR on a different server or a standalone server.
Does HACMP support non-IBM hardware or operating systems?
Yes. HACMP for AIX 5L supports the hardware and operating systems as specified in the manual where HACMP V5.4 includes support for Red Hat and SUSE Linux.
What is nmon tool do?
The nmon tool is designed for AIX and Linux performance specialists to use for monitoring and analyzing performance data, including:
- CPU utilization
- Memory use
- Kernel statistics and run queue information
- Disks I/O rates, transfers, and read/write ratios
- Free space on file systems
- Disk adapters
- Network I/O rates, transfers, and read/write ratios
- Paging space and paging rates
- CPU and AIX specification
- Top processors
- IBM HTTP Web cache
- User-defined disk groups
- Machine details and resources
- Asynchronous I/O — AIX only
- Workload Manager (WLM) — AIX only
- IBM TotalStorage® Enterprise Storage Server® (ESS) disks — AIX only
- Network File System (NFS)
- Dynamic LPAR (DLPAR) changes — only pSeries p5 and OpenPower for either AIX or Linux
Also included is a new tool to generate graphs from the nmon output and create .gif files that can be displayed on a Web site.
What is Logical Volume Manager(LVM) means?
The set of operating system commands, library subroutines and other tools that allow you to establish and control logical volume storage is called the Logical Volume Manager (LVM).
What is a Logical partition?
A logical partition (LPAR) is the division of a computer’s processors, memory, and hardware resources into multiple environments so that each environment can be operated independently with its own operating system and applications.
Explain Network File Systems(NFS)?
The Network File System (NFS) is a distributed file system that allows users to access files and directories of remote servers as if they were local. Suppose,
Server A, that makes its file systems, directories, and other resources available for remote access. Client’s computers, or their processes, that use a server’s resources.
Export the act of making file systems available to remote clients.
Mount the act of a client accessing the file systems that a server exports.
What is Network Information Service (NIS)?
NIS was developed to simplify the task of administrating a number of machines over a network. In particular was the requirement to maintain copies of common files (e.g. password, group and host) across different systems.
What is software RAID Levels do?
Redundant Arrays of Independent Disks (RAID) is formally defined as a method to store data on any type of disk medium.
The Light Directory Access Protocol (LDAP) defines a standard method for accessing and updating information in a directory (a database) either locally or remotely in a client-server model.