Unix Administration Guntis Barzdins.

Unix Administration Guntis Barzdins

SYS ADMIN TASKS Linux System Administration Setting the Run Level
System Services User Management Network Settings Scheduling Jobs Quota Management Backup and Restore Adding and Removing software/packages Setting a Printer Monitoring the system (general, logs) Monitoring any specific services running. Eg. DNS, DHCP, Web, NIS, NPT, Proxy etc. Run level – nav vairs gluži aktuāli (init slaidos kādēļ) Quota management – bija vairāk aktuāli mainframe laikos un tagad daudz (lietotāju (kuru reāli lieto dažādi lietotāji kā atšķirīgi unix konti) sistēmās

Have you used UNIX before?
Which OS did Apple choose when it needed a stable OS layer for its Mac OSX? Which OS made the biggest impact to the online lives as you know it today? Use as ice-breaking slide Unix is not alien to you. You're using it, but it's just that What do they have in common? Why will these folks, arguably the best IT minds in the world, use an OS designed in the 1970? These services run on Unix. Apple choose BSD. Yahoo is runing on BSD. Google is running on BSD. These are unix variations.

Process Manipulation Once you run a program (e.g. vi, myprog,...), that program will suspend the terminal you called it in (the terminal will not be receiving input from you). You can start the program in the background to avoid this: myprog & You can suspend a program that is running and send it to background, if you already started it: Ctrl-z (to suspend) bg (sends the suspended program to the background) ps (show running processes) top (monitor running processes) kill (kill processes) & (send process to background) bg (send process to background) fg (get process from background) Ctrl+c (terminate process) Ctrl+z (suspend process) Background izvads stderr un stdout paliek, līdz ar to, ja programma visu laiku kaut ko izvada, tad šī konsole paliek nelietojama Suspend – aptur darbību, bet kontekstu saglabā Ps, top – daudz dažādas opcijas Kill – faktiski nosūta signālu procesam, kas var procesu nogalināt

Intrusion Detection System (IDS)
Open Source Tripwire – is a file integrity- checking program for UNIX/Linux operating systems Host-based Software that alerts you when important files change Tripwire keeps a hash value for each designated file When a file is altered/deleted, tripwire will have a new hash value that is different than the original Replaced by more advanced HIDS: OSSEC, Samhain, AIDE Viena no pirmajām un visvienkāršākajām sistēmām

Tripwire tutorial in a slide
Initial setup download / build / install it modify policy file (e.g. remove unnecessary files) # vi /etc/tripwire/twpol.txt generate policy file # twadmin –create-polfile /etc/tripwire/twpol.txt build initial database # tripwire –init check periodically # tripwire –check reconcile differences (e.g. software installation) # tripwire –update –accept-all –twrfile report_file Vienkārša sistēma, glabā čēksummas lokāli, labākā aizsardzība ir parole atslēgai vai atslēgas fails, kas paraksta datubāzi. Ja paraksts nav izmantots (kā piemērā) vai arī tiek nozagts, tad uzbrucējs var modificēt datubāži, ka viss izskatās labi, tādēļ šādu sistēmu enterprise mazāk izmanto. Ir daudz labākas open source HIDS, kurās ir arī klienta/servera funkcionalitāti, kas glabā datu bāzi droši un attālināti.

LINUX Firewall Linux Security
Visos gadījumos, kad ir redzams šāds vai līdzīgs logs, tas vienkārši tiek translēts uz kodola firewall iptables/pf, kam ir nepieciešamas root tiesības, bet visa programmatūra, kas attēlā, tiek laista ar root tiesībām. Daudzos gadījumos unix firewall nav nepieciešams, nekas slikts nenotiek, ja saņemam paketes, kas adresētas kaut kam, kas nav iedarbināts.

SELinux Linux Security Originally created by NSA to meet US DoD MAC
Malicious or broken software can have root-level access to the entire system by running as a root process. SELinux (Security Enhanced Linux) provides enhanced security. Through SELinux policies, a process can be granted just the permissions it needs to be functional, thus reducing the risk SELINUX can take one of these three values enforcing - SELinux security policy is enforced. permissive - SELinux prints warnings instead of enforcing. disabled - SELinux is fully disabled. United States Department of Defense-style mandatory access controls, pēc defaulta ir DAC Android style – abstrakcijas Paredzēts, lai aizsargātu sistēmu no kompromitētas programmas Vienkāršāks risinājums mūsdienās, katru servisu uzturēt savā virtuālā mašīnā Enforcing – ja programma pēkšņi izmanto kaut ko, ko neesam paredzējuši, tas tiek liegts. Permissive tiek izmantots, lai iegūtu priekšstatu par

SELinux Configuration
Linux Security SELinux Configuration Šis logs un visi citi translējas uz rīkiem un failiem. Sistēma ir sarežģīta. Empīriski novērtējums, ja daudz unix mašīnu un n unix adminu, tad vēl n adminus vajag selinux.

AppArmor Less complex and less secure
Popular in user oriented distributions (Ubuntu, SUSE), enabled for some potentially vulnerable services by default Bundle software packages with AppArmor profiles Can create profile file by launching application in learning mode, can make secure enough profile if application not already compromised Capabilities: FS open/read/write different modes, networking (all/tcp/udp), executability etc.

Log files On linux, you can go to /var/log Depends on the application
Information shown in log files depend on the debug level you defined Parasti unixos ir /var/log, kur ir gan programmas, gan pēc notikumu grupām Ja vajag drošību, tad šis mehānisms, nav pietiekami ir jāieslēdz attālinātu logošanu uz drošiem serveriem, syslog servisi to atļauj. Ja tiek kompromitēta sistēma arī log faili var tikt kompromitutēti.

Configuring Disk Quotas
Linux System Administration Configuring Disk Quotas To implement disk quotas, use the following steps: Enable quotas per file system by modifying /etc/fstab Remount the file system(s) Create the quota files and generate the disk usage table Assign quotas Šobrīd izmanto mazāk, agrāk bija nepieciešams, jo ir mainfreimi un daudz lietotāju sistēmas, kur viens lietotājs varēja aizpildīt visu disku un traucēt sistēmas darbību. Šobrīd izmanto, ja sistēmā ir trešās puses lietotāji, kuriem ir kādi konkrēti resursi iedalīti, piemēram, shared hosting accounts.

Linux System Administration Configuring Disk Quotas Enabling Quotas: Edit fstab to enable usrquota LABEL=/ / ext3 defaults LABEL=/boot /boot ext3 defaults LABEL=/users /users ext3 exec,dev,suid,rw,usrquota LABEL=/var /var ext3 defaults LABEL=SWAP-sda5 swap swap defaults Jāpieliek usrquota pie opcijām, vēl viena opcija ir grpquota BSD UFS – unix fs, root rezervēts

Linux System Administration Configuring Disk Quotas Remounting the File Systems: Issue the umount command followed by the mount command to remount the file system in which quota has been implemented (umount /users;mount /users) Creating the Quota Database Files: Use quotacheck command to create quota.user file quotacheck -cu /users Assigning Quotas per User: assigning the disk quotas with the edquota command (edquota <username>) Disk quotas for user web_cc (uid 524): Filesystem blocks soft hard inodes soft hard /dev/sdb blocks: 1k blocks inodes: number of files and directories that can be created soft: Max number of blocks/inodes user may have on partition before warning is issued and grace persiod countdown begins. If set to "0" (zero) then no limit is enforced. hard: Max number of blocks/inodes user may have on partition.

Linux Filesystem Management
Linux Commands Linux Filesystem Management badblocks Used to search a disk or partition for badblocks. (badblocks device) (badblocks hda) df Shows the disk free space on one or more filesystems. (df –k, df -h) du Shows how much disk space a directory and all its files contain. (du <directory>, du –sk <directory>, du – sh <directory>) Find out which users use most space etc. $ du /home -d 1 | sort fsck Filesystem check. Must not be run on a mounted file system. (fsck <filesystem>) Fsck - ja nav atmontēts disks – sistēmas crash, power failure etc., tad ir jānočeko un jāsalabo diski single user mode.

Linux Filesystem Management
Linux Commands Linux Filesystem Management sync Synchronize data on disk with memory. `sync' writes any data buffered in memory out to disk. mount Used to mount a filesystem. Complement is umount. (mount <filesystem>, mount –a) umount Unmounts a filesystem. Complement is mount. (umount <filesystem>) Sync – ar roku mūsdienas vairs netiek lietots standartā

Native UNIX Backup Utilities
UNIX Systems include 3 core utilities that allow you to backup files to tape or disk. tar (very simple to use) cpio (a bit more complex) dump (most complex of the three) Dump – ir failsistēmas bakupošana, fstab failos vēl joprojām ir saglabājusies dump ocpija, bet to reti lieto

Using the tar Utility for Backup
tar usage: tar [x|c]vf [tape device name] [files or directory] Where: x = extract from a tape c = compress onto tape j = use bzip compression z = use gzip compression (just like when we tar and untar regular .tar files) Tar – tape archive, oriģināli vienkārši saliek visus failus vienā failā, lai varētu secīgi lasīt un rakstīt uz lentas

Other UNIX Backup Utilities
cpio – has the ability to detect I/O errors during backup that tar cannot detect. Also has the ability to do things like specify wildcard patters during restore. dump – very fast, detects I/O errors, allows you to perform incremental backups. Šie retāk lietoti

TAR CPIO DUMP Simplicity of Invocation Very Simple (tar c files) Needs find to specify file names Simple. Few Options Recover from I/O errors? None. Write your own utility Resync Option on HP-UX will cause some data loss Automatically skips over bad section Backup special files Later Revisions Yes Multi-volume backup Backup across network? Using rsh only Append files to backup Yes, (tar –r) No Multiple Independent Backups on Single Tape Ease of listing files on the volume Difficult, Must search entire backup ( tar –t ) ( cpio –it ) Simple, Index at front ( restore –t ) Ease and speed of finding a particular file Difficult, No wildcards, Must search entire volume Moderate, Wildcards, Must search entire volume Interactive. Very easy with commands like cd, ls Incremental backup Must use find to locate new/modified files Incremental of whole filesystem only, Mult. Levels List files as they are being backed up tar cvf 2>logfile cpio –v 2>logfile Only after backup with restore –t >logfile (Dump can show % complete, though.) Backup based on other criteria Find can use multiple criteria Restore absolute path names to relative location Only by using chroot Limited with cpio -I Always relative to current working directory Interactive decision on restore Yes or No possible with tar –w Can specify new path or name on each file Specify individual files in interactive mode Compatibility Multiple platform Multiple platform with ASCII header, not always portable Readable between some platforms, but cannot be relied on Primary usefulness Individual user backup, transfer files between filesystems System backup, transfer files between filesystems System backup Volume efficiency Medium, usually limited to 10k block size Medium, usually only 5K block size, but can specify larger size on some OSs High, can usually specify up to maximum block size of device Wildcards on restore Only in interactive mode Simplicity of selecting files for backup from numerous directories Low, must specify each independent directory, subdirectories included Medium, find options None, will backup one and only one filesystem Specifying directory on restore get files in that directory No, must use "path/*" Stop reading tape after a restored file is found Will stop reading tape as soon as last file is found Track deleted files If you restore with –r, files deleted before last incremental dump will be deleted. Filesystem efficiency Better Worst (files get a stat from both find and cpio) Best Limit on path length (Tests done with Solaris native utils 7/99.) 155 characters. Complains "prefix is greater than 155 characters." Gtar has slight workaround. 255 characters. Doesn’t complain. Just truncates pathname to 255 char’s. 1056 characters. Likelihood that file exists in TOC but not in archive Low Medium (since TOC is made first)

rsync Over network and filesystem Secure through SSH
Both ends require rsync executable, no services or daemons required Incremental backup Delta encoding Only changed parts of files transmitted Example rsync -avz /backups/server1 Many options Jaunāks un daudz populārāks par iepriekšējiem

Lost Root Passwd If you have Lilo installed, type
LILO: linux init 1 Change the root passwd, reboot again If you have installed grub Type ‘e’ to go to edit mode, add init 1 argument at the end Boot with LiveCD (default Ubuntu etc.) Mount the disk chroot into mounted disk passwd Reboot and remove CD

Linux Services Linux System Administration
There are 113 daemons, Out of them, the following are most widely used: apmd : Power Management autofs : Automount services crond : Periodic Command Scheduler cups : Common Unix Printing System dhcpd : The DHCP server dovecot : IMAP (Internet Message Access Protocol) and POP3 (Post Office Protocol) server gpm : Mouse httpd : Apache Web server

iptables : Kernel based Packet Filtering firewall kudzu: Finds new Hardware mysqld : MySQL server named : BIND server network : Networking nfs : Network File Share nfslock : NFS file locking ntpd : NTP (Network Time Protocol) server portmap : RPC (Remote Procedure Call) support postgresql : The Postgresql Database Engine

sendmail : Sendmail Mail Server smb : Samba Network Services snmpd : Simple Network Management Protocol squid : Squid Proxy Server sshd : Open SSH and SFTP server syslog : System Logging xinetd : Provides support for telnet, ftp, talk, tftp etc. ypbind : NIS Server

Automating Unix Administration
You don’t want to spend the whole day making sure that all servers/workstations and its services are fine Use monitoring tools that can alert you for any problem in the network mon, nagios, cacti, angel Zabbix – Latvian product Create scripts to check the status of servers/services and use cron to run it periodically Mail the result to admin Zabbix ir piemērs open source biznesam, veidojam labu un advancētu open source produktu un pārdodam tam supportu

Example script Pārbaudam 15 sistēmas, ja nepingojas, tad sūtam emailu.
#!/bin/sh machine="sunfire" down= i=0 while [ $i -le 15 ] do sun=$machine"$i" /usr/sbin/ping $sun > /dev/null if [ $? -ne 0 ] then down="$down:$sun" fi i=`echo "$i+1" | bc -l` done if [ -n "$down" ] echo $down | tr : '\012' | /usr/ucb/mail -s "DOWN machines" exit 0 Pārbaudam 15 sistēmas, ja nepingojas, tad sūtam u.

NFS Architecture VFS layer hides differences between OS’s
It doesn’t matter what OS the client or server implements, UNIX or Windows. As long as the file systems are compliant with the file system model offered by NFS. Operations on VFS are either passed to local FS or to NFS Client, which handles files at the remote server. All client-server communication is done through RPCs, with client and server stubs. Implemented with either UDP or TCP. VFS Layer is standard for most DFS. VFS Layer hides differences between OS’s. It doesn’t matter what OS the client or server implements. As long as the file systems are compliant with the FS model offered by NFS. for example MS-DOS with its short file names can’t be used to implement NFS with full transparency. Operations on VFS are either passed to local FS or to NFS Client. NFS Client which handles files at the remote server. Then the NFS Server converts requests to regular VFS operations. All client-server communication is done through RPCs, with client and server stubs.

NFS Architecture VFS Layer is standard for most DFS.
VFS Layer hides differences between OS’s. It doesn’t matter what OS the client or server implements, UNIX or Windows. As long as the file systems are compliant with the FS model offered by NFS. MS-DOS for example with its short file names can’t be used to implement NFS with full transparency. Operations on VFS are either passed to local FS or to NFS Client. NFS Client which handles files at the remote server. All client-server communication is done through RPCs, with client and server stubs. NFS Server converts requests to regular VFS operations.

Stateless vs. Stateful Version 3:
Unlike most DFS, v3 of NFS is stateless. The good thing about this is: No worrying about server crashes, no need for a recovery phase to bring server back to previous state. Each request contains sufficient information to be completely processed without regard to other requests. NFS clients, however, are not stateless. NFS clients hold modified data that has not been flushed to the server as well as cache file handles and attributes. Clients typically use attribute information, such as file modification time, to validate cached information. “NFS servers are stupid and NFS clients are smart” A stateful protocol means that cache consistency is easier. Because server maintains information on files as used by its clients. Server can do an RPC to a client – callback, this can only be done on stateful server because the server needs to be able to keep track of its clients.

NFS (Network File System)
RCP request Action Idempotent GETATTR Get file attribute YES SETATTR Set file attribute LOOKUP File name search ACCESS Check access READLINK Read from symbolic link READ Read file WRITE Write to the file COMMIT Fix server cache data to the disk CREATE Create file NO REMOVE Remove file RENAME Rename file

RCP request Action Idempotent LINK Create hard link NO SYMLINK Create symbolic link MKNOD Create special node MKDIR Crate directory RMDIR Remove directory READDIR Read directory YES READDIRPLUS Extended directory read FSSTAT Get FS dynamic attribute FSINFO Get FS static attribute PATHCONF Get POSIX information

Stateless protocol problems: Local file systems have state. Shared lock’s implemented by user space daemon rcp.lockd Performance problems, because all file system modification commands should be fixed on disks before RPC request can be positively answered. In most cases it is 3 I/O operations. In NFSv3 protocol there is asynchronous writes. Implemented using cookies to control server state during asynchronous writes.

FreeBSD NFS implementation
There are 3 type of leases: Non-cache lease – define that all file system operations should be take synchronously with server Read cache lease – let client cache data, not allow to change file. Write cache lease – let client to cache write operations for lease time. So if client cache write data, then this data will not be written to the server synchronously. When lease time coming to the end client will try to get another lease, but if it’s not possible, then data have to be written to the server.

FreeBSD NFS implementation (read cache lease)
Server Client B Client A Read req. + lease Read sys. call Time Read cache lease for client A Answer Read req. (cache miss) Read sys. Call (from cache) Answer Lease timeout Lease expired Read sys. call Read lease req. Answer with same ctime Read req. + lease Read sys. call ctime the same - cache valid Answer Client B added to lease Read sys. Call (from cache) Read req. (cache miss) Read sys. call Read req. (cache miss) Answer Lease timeout Answer Lease timeout

FreeBSD NFS implementation (write cache lease)
Server Client B Write cached lease Write system call Write cached lease for client B Answer (write cache lease) Write system call (cached leaved records) Write cached lease req. before previous lease expired. Lease update Get record lease Answer (write cache lease) System call Lease timeout record Lease expired Lease expiration Stopped for a moment because of records answer record Time answer Write_slack seconds After last records

FreeBSD NFS implementation (non-cache lease)
Client B Client A Server Read req. + lease Read sys. call req. Time Read cache lease for A client Read req. (from cache) Read req. (miss cache) answer Lease expired answer Get write cache lease Lease timeout Write sys. call req. Write sys. call (async write cached) Lease request Read sys. call req. Cleanup req. record Write cached data to server answer record answer Release msg. Get write cache lease Write sys. call req. Answer (non-cache lease) Read sys. call req. (non-cache lease mode) Read req. Answer (non-cache lease) record Synchronous Writes wihout cache Read data answer

Starting up NFS There are three key things you need to start on Linux to make NFS work. /usr/sbin/rpc.portmap /usr/sbin/rpc.mountd /usr/sbin/rpc.nfsd These things should start up automatically at boot time. The file that makes this happen is "/etc/rc.d/rc.inet2" rpcinfo -p localhost program vers proto port 2 tcp 111 portmapper 2 udp 111 portmapper 1 udp 679 mountd 1 tcp 681 mountd 2 udp 2049 nfs 2 tcp 2049 nfs

Exporting File System To make parts of your file system accessible over the network to other systems The /etc/exports file must be set up to define which of the local directories will be available to remote users and how each is used # sample /etc/exports file /home/yourname (rw) /master(rw) trusty(rw,no_root_squash) /projects proj*.local.domain(rw) /usr /home/joe pc001(rw,all_squash,anonuid=150,anongid=100) /pub (ro,insecure,all_squash) /pub/private (noaccess) stop and restart the server # etc/rc.d/init.d/nfs stop # etc/rc.s/init.d/nfs start

The NFS Server Started though rc script: /etc/rc.d/init.d/nfs Must be started after: /etc/rc.d/init.d/portmap Uses these RPC daemons in /usr/sbin: rpc.nfsd – main component of NFS system rcp.mountd – handles mount requests rpc.quotad – allows for quota enforcement via NFS. All of which are started in the nfs rc script when the system starts /etc/exports – the main server configuration file Above utilities are part of knfsd package .rpm package on Linux.

/etc/exports Contains information about the directory paths and partitions that are sharable and hosts they can be shared with. i.e. “Any host from .rutgers.edu can access the /home/documents directory on my server” Entry format: /dir/to/export client1(permissions) client2 (permissions) Sample entry: /tmp iti.rutgers.edu(rw) (ro) Need to run exportfs to inform NFS server process about changes in /etc/exports: > /usr/sbin/exportfs –a (exports all entries)

The NFS Client Requires knfsd-clients .rpm package on Linux.
Necessary services started from: /etc/rc.d/init.d/nfslock RPC daemons in /sbin handle file locking between client and server: rpc.locked rpc.statd All are started from the nfslock rc script automatically Allows clients to mount remote file systems either using the mount command or by placing an entry in the /etc/fstab file.

Local and remote file systems accessible on an NFS client
mount –t nfs Server1:/export/people /usr/students mount –t nfs Server2:/nfs/users /usr/staff

FUSE (Filesystem in Userspace)
Lets non-privileged users create their own file systems without editing kernel code. Vajadzība pēc iespējas strādāt lokāli ar tādām lietām, kas īsti nav lokāli izmantojamas FS

FUSE Allows to implement anything with file write and read operations and provide it as file system Encryption – EncFS, TrueCrypt, etc. Network protocols – SSH, FTP, SFTP, etc. Cloud storage – Dropbox and every other kind RAM disk

SMB SMB is Microsoft’s protocol to share files and printers
Also renamed CIFS (Common Internet File System) Client/Server, no location transparency Not the same as Samba: an open source implementation of SMB primarily found on UNIX systems (Linux) SMB usually runs on NetBIOS (naming + sessions + datagram) NetBIOS + SMB developed for LAN use A number of other services run on top of SMB In particular MS-RPC, a modified variant of DCE-RPC Authentication for SMB handled by the NT Domains suite of protocols, running on top of MS-RPC NT-Domain MS-RPC SMB NetBIOS TCP/IP To know more: Timothy D Evans, NetBIOS, NetBEUI, NBF, NBT, NBIPX, SMB, CIFS Networking

Samba Services File sharing. Printer sharing. Client authentication.

SMB Protocol Request/response. Runs atop TCP/IP.
E.g., file and print operations. Open close, read, write, delete, etc. Queuing/dequeing files in printer spool. Doma ir tāda, ka var izmantot unix serveri, kas apkalpo tīklu ar Windows datoriem.

Network Booting No need for harddisk(or harddisk with Linux) on every host High level work flow The system boots up, may be with floppy (could be with hard disk also) Sends dhcp request for IP number, gets one Mounts the root file system over NFS

Requirements for Network Booting
Setup an LAN infrastructure Need to setup nfs server Need to setup dhcp server Build a kernel image for network booting

Setup an LAN infrastructure
Hub Ethernet Cable Ethernet Cable NFS server Your m/c to be booted Your host, NFS server and DHCP server should be on same LAN

Setup nfs server / 10.114.7.115(rw,no_root_squash)
Edit /etc/exports file before starting the nfs server. / (rw,no_root_squash) This will export all files with root r/w to host Save your exports file and from the prompt execute exportfs command Start the nfs server (nfs daemon) E.g. /etc/rc.d/inid.d/nfs start Mount the root file system using loop mount. E.g. If root_fs is your root file system file loop mount it on the server to a ditectory using the mount command. E.g. mount –o <root_fs path> <directory path>

Setup dhcp server Add in your /etc/dhcpd.conf before starting the dhcp server. Set the correct MAC address in /etc/dhcpd.conf as follows: subnet <subnet address e.g > netmask { } subnet netmask { host master { hardware Ethernet <Mac address of your Ethernet card>; fixed-address <IP address of your machine e.g >; option root-path <your root path>”; Save your /etc/dhcpd.conf file start the dhcpd dameon by “/etc/rc.d/init.d/dhcpd start” command Root-path – norāde uz klient nfs root direktoriju

Build a kernel image for network booting
Linux Kernel compilation steps: Assumptions: machine x86 (i386); boot loader lilo. Get plain vanilla kernel from Explode it into a directory (better if can do it in /usr/src/) => tar -zxvf linux-2.x.xx.tar.gz Optional: create a symbolic link ln -s linux-2.x.xx linux cd to linux directory cd /usr/src/linux or cd /usr/src/linux-2.x.xx Select the components support by make menuconfig or make xconfig - save the configuration Select IP:BOOTP support from Networking options In File system -> Network File System -> Select NFS File system support and Root file system on NFS Do Make dep bzImage Make modules modules_install

Build a kernel image for network booting…
Copy the /usr/src/linux/arch/i386/boot/bzImage to /boot Do mkbootdisk with new kernel as argument Optional take a coffee or tea break ?

Just imagine if one day... Your CEO announces:
Company is changing name from "Windoze" to "UsefulNix" TOMORROW! Your "small part": Update the company website* to reflect that! Can you deliver this in time? *: About 20,000 html files. Solaris - > Oracle pēc nopirkšanas, viens no smagākajiem updeitiem visur nomainīt

Demo (1/2) - UNIX vs. Window
Task 1 : Open a file. Find occurrences of "Windoze". Windows: use Ctrl-F at any text editor. UNIX: grep -l Windoze fileName Task 2 : Find all files in folder A containing "html". Windows: Arggghhhh!!! Open all files and check? UNIX: find A -type f | xargs grep -l Windoze take note: create own file , with line breaks ,

Demo (2/2) - UNIX vs. Window
Task 3 : Open a file. Replace "Windoze" by "UsefulNIX" Windows: Use Ctrl + H at any text editor UNIX: perl -pi -e 's/Windoze/UsefulNIX/g' fileName Task 4 : Find all files in folder A with "html", and replace by "UsefulNIX" Windows: haizzz.... UNIX: find A -type f | xargs grep -l Windoze | xargs perl -pi -e 's/Windoze/UsefulNIX/g' See how powerful UNIX is ^^ & the idea of "achieving complex tasks through small toys“ Let's learn UNIX !!!

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