System Administration PC-Pools

account An account on a “UNIX”-System. It consists of the pair of username and user ID, also called login and UID. BSD Berkeley Software Distribution Family of mostly free unix derivates like FreeBSD, OpenBSD and NetBSD. Bash (Bourne-again shell) is the standard shell in many unix and linux systems. Contrasting to the PowerShell/PowerShell Core is the bash not object-oriented, but purely text-based. C is the programming language in which the platform independent part of the Linux kernel and most of the applications has been developed. CLI (Command Line Interface). A programme that enables the user to issue commands to the operating system. Under Linux the CLI is realized in the form of the different shell-implementations. Compiler A compiler serves as a tool for the creation of programmes. More precisely, it translates source code into object files. Copy-On-Write Describes a feature of file systems where blocks are not over-written directly, but instead a copy of the new data is stored in a different block. After finishing a new block, the corresponding pointer is adjusted. Hence, in the case of a system crash during the write-operation no inconsistent file system state is created. Only the data that was written in that moment would be lost, but the previous version of the block is still intact. Apart from that, this concept makes the easy and fast creation of snapshots possible. CPU (Central Processing Unit). The primary micro-processor. A processor is an (albeit very small and freely) programmable arithmetic unit, i. e. a machine or electrical circuit that controls other machines or electrical circuits according to the instructions it is being passed. Dataset (in the context of ZFS) is a term for ZFS-file systems, volumes and snapshots. Datasets are organised in a hereditary hierarchy and always assigned to a zpool. They serve as structuring unit of the pool and can be tailored to many different applications. The compression, check sum algorithm, logical block size and many more features and properties of any dataset can be changed individually by setting corresponding parameters. All datasets share the storage space of the whole pool, hence they should not be considered as a partition with its own storage space. Daemon processes processes running in the background and mostly performing special tasks. Device (file) A device interface that is mapped to a device file in the virtual file system. These files usually reside under the directory /dev. Debian Debian Linux is also a collaboratively developed free operating system. Debian GNU/Linux is based on the basic system tools of the GNU project and the Linux kernel. ext2/ext3/ext4 The file systems primarily used under linux. The newer ext3 featuires journaling, in contrast to ext2, however it is backwards-compatible. Using an ext2-driver one can still access an ext3 partition. ext4 is has been developed as successor to ext3. FIFO (First-In-First-Out). A FIFO is a queue. Data that has been written into it has to be retrieved in the same order. Firewall A computer or application that protectes the local network from attacks from the internet. FQDN (Fully Qualified Domain Name). The full domain name of a system, consisting of hostname and domain. The full name of a (web) domain is called the Fully Qualified Domain Name (FQDN). In that case, it is an absolute address. The FQDN www.example.com. consists of: 3rd-level-label. 2nd-level-label. Top-Level-Domain(com). and hence is: www.example.com FTP (File Transfer Protocol). A protocol for the communication with file servers. GPL (GNU General Public License). Licence under which linux and a lot of other free software is distributed. HTTP (HyperText Transfer Protocol). A protocol describing the interaction with web-servers. HTTPS HTTPS (HTTP Secure) is an encrypted version of HTTP. Most of the times it uses SSL (en-US) or TLS in order to encrypt the whole communication between a client and a server. This safe connection enables clients to safely exchange sensitive information with the server, like e. g. in online banking or online shopping. Interpreter An interpreter executes a script written in a programming language without having to compile it beforehand. ISO 9660 This standard describes a file system for CD-ROMs and DVDs. Typical characteristics are the limits on the length of filenames. Also there is no information about the file owners and permissions. Journaling In journaling file systems, every transaction is logged, so that after a crash the often-times cumbersome repair of the file system can be omitted. Kernel The kernel is the core component of the operating system and responsible for important tasks like process and memory management or supporting the hardware. Kernel-Module Loadable kernel modules (LKM) are components that can be dynamically integrated into the kernel and often provide driver code. Thanks to such LKMs a re-compilation of the kernel is often not necessary. Kernelspace Memory region in the RAM for the kernel and all kernel modules, like hardware drivers. LKM (Loadable Kernel Module). See Kernel-Module. Linux is an operating system based on the linux (operating system) kernel an free GNU software. Linus was developed in 1991 by the Finn Linus Torvalds on the basis of the operating system UNIX. Multitasking Ability to execute multiple processes simultaneously. Multiuser A multiuser systems is an operating system that is capable of providing and keeping seperated working environments for multiple users. NFS The Network File System (NFS) is a protocol developed by Sun Microsystems which allows accessing files over a network connection. NNTP NNTP (Network News Transfer Protocol) is a transfer protocol for new in newsgroups. It is used e. g. in Usenet. NTP The Network Time Protocol (NTP) is a standard for the synchronization of clocks in computer systems over packet-based communication networks. NTP uses the connection-less transfer protocol UDP or the connection-oriented TCP. Is was developed specifically to make the transmission of reliable time stamps possible over networks with variable packet runtime. Open Source Movement for the promotion of free software. Free software is defined by its free use and the availability of the source code. Proxyserver A proxy server is a server between many clients and one server. In general its task is to buffer requests so that the server is not being overloaded. Process A process in Linux is ideally representing a running programme. Apart from the executable programme code also the environment, consisting but not restricted to shell variables, is included in this concept. Pseudo File System A file system that typically resides in memory and has to be access via a pseudo interface. Examples are procfs and swapfs. Quota Disk Quota (quite literally) is a limit for the storage on storage devices like hard drives, that a single user or group of users can use. It limits the storage use of a user. RAM (Random Access Memory). The main memory. ROM (Read Only Memory). A memory that can only be written once. It is e. g. installed on the mainboard for storing the BIOS. SMB A protocol for file shares in a network. Primarily used in the Windows ecosystem. SMTP (Simple Mail Transfer Protocol). The standard protocol for sending E-mail. Snapshot freezes the state of a filesystem at a certain point in time. If data in the file system is changed, both the current version and the version of the snapshot are stored. At a later time either the state of the snapshot can be restored ore single files of the snapshot can be accessed for recovery purposes. Secure Shell (SSH) is a protocol and the corresponding client and server programmes for establishing an encrypted network connection. SHH features mutual authentication and an encrypted file transfer. Initially only for UNIX-based systems, there are nowadays also implementations for Windows and others. Swap Parts of the main memory relocated onto the hard drive. Syscall A system-call, i. e. a call of a particular kernel function by a programme running in user space. TCP/IP Transmission Control Protocol/Internet Protocol The TCP/IP-protocol family consists of many important protocols for network communication. The Transmission Control Protocol (TCP) is a network protocol which defines how data should be exchanged between network components. Unlike the connection-less UDP (User Datagram Protocol) in TCP a connection is established between the end-points of a network connection (sockets). Using that connection data can be transmitted in both directions. Most of the times TCP is stacked onto the IP (Internet Protocol). That is why sometimes people (mostly imprecisely) talk about a “TCP/IP”-protocol. Ubuntu also Ubuntu Linux, is a Linux distribution derived from Debian. The name comes from the Nguni philosophy of ubuntu, which means something in the direction of “humanity to others.” Userspace Part of the RAM which is used for all programmes and data that are not directly associated to the kernel. Hence, these programmes have no access to the memory region of the kernel. VFS (Virtual File System). The virtual file system forms the basis of file system management. All other file systems are integrated by so-called mount points and are hence transparent to the user. WLAN (Wireless LAN). Connect to the network over radio connections. X11 The X window system 11 release 7 (X11R7) provides a graphical user interface for Unix systems. Zombie-Process A process which has already terminated but still resides in memory. That way, the parent process can still evaluate the return status of the process later even though it has been neglected at the time. ZFS ZFS is a transactional file system developed by Sun Microsystems. zpool Concept of ZFS. In practical applications several physical storage devices are pooled into logical units, the zpools, which can optionally be configured more fail-safe. In order to generate a pool stretching over multple hard drives and then create partitions on it, only two relatively simple instructions are needed. Partitioning, creating the logical volume and subsequent mounting in an existing file systems is done automatically.