Linux-LPIC201-Summary

I got LPIC-level1 last week, so I will continue to take level2. Therefore, the main points of the test range are summarized below.

1. Capacity planning

Resource utilization

• top ――You can see it comprehensively
• vmstat --Memory / virtual memory status --vmstat 5 3 (output 3 times every 5 seconds) --r-> Number of processes waiting to be executed --b-> Number of non-interruptible processes (preferably 0) --wa-> cpu IO wait time --buff / cache-> buffer cache / page cache (at most)
• iostat
• iotop --View I / O like top IO information for each process
• sar --system activity report-> System statistics report, multi-functional --sar -b -f / var / log / sa / saXX-> View XX day report
• sadf --different format-> sadc log output in CSV, TSV, XML, etc. (combined with tr, etc.)
• uptime
• w --Understanding logged-in users and processes
• ps
• pstree
• lsof --Process, port status
• free --Memory and swap --There is no problem if the cache is large even if there is little free -/ proc / meminfo-> Detailed memory information
• df --Easy to understand disk usage for each file system
• netstat
• ss --Almost the same as an alternative to netstat
• netserver --Server side
• netperf --Client side
• iptraf --Monitor traffic

Resource monitoring tool (I can't remember)

• collected
• Nagios
• MRTG --Traffic Grapher, so it graphs traffic
• Cacti
• Icinga2

Regarding other resource management

--Bottleneck by focusing on IO on a specific partition-> Try changing to faster storage --Rebuild kernel / adjust kernel parameters --swapon -s-> Check swap (/ proc / swaps)

2. Linux kernel

version

--4.9-rc1-> rc is Release Candidate (development version) --How to check the version ① ʻuname -r` ② / proc / version file ③ View Makefile

Kernel image

Kernel module

--Some functions are separated from the kernel and modularized (.ko)-> The kernel becomes compact and saves boot time and memory.

• lsmod --Same as / proc / modules
• modinfo
• insmod
• rmmod
• modprobe --Loads / unloads while resolving dependencies --depmod-> modules.dep file (module1.ko: module2.ko module3.ko) --I want to preprocess or add an alias-> Set in /etc/modprobe.conf or /etc/modprove.d/ file
• ex. alias eth0 r7257 --kmod-> Kernel feature automatically loads modules when needed

Kernel compilation

--Source code-> / usr / src --How to upgrade-> ① cp / boot / congig ... x86-64 .config (copy the previous configuration file to .config) -> ②make oldconfig --Kernel configuration-> make menuconfig --Compile-> make --Kernel module and kernel installation-> make modules_install-> make install --Since the image is created in / boot, use the default kernel. --DKMS-> Dynamic Kernel Module Support (automatically builds a third party kernel module)

• make clean make mrproper

Kernel parameters (/ proc / sys /)

--sysctl [-w] net.ipv4.ip_forward = 1 (disappears on reboot) / Write to /etc/sysctl.conf (persistent)

Initial ramdisk

--initrd / initramfs (cpio archive + compression) --Create initial ramdisk-> mkinitrd / mkinitramfs --Initramfs can be created under / boot with the latest CentOS-> dracut command

Kernel management and problem solving

• lsdev
• lspci --lspci -s 2: 0-> Bus 2 and slot 0
• lsusb --Block device-> b / block unit / random access / HDD, RAM disk, RAID volume, etc. --Character device-> c / Character unit / Random not possible / Keyboard, mouse, terminal, etc. --I want to see the devices recognized by the kernel-> / proc / devices --udev / sysfs-> /etc/udev/rules.d/60-raw.rules etc. --Check how sysfs handles the device-> ʻudevadm info (used for identification) --rules file identification key = match value-> device file created with specified rules --Monitor device detection-> ʻudevadm monitor

3. System boot

Startup process

• BIOS/UEFI ---> MBR (part of boot loader + partition table) / GPT ---> MBR bootloader launches second stage bootloader ---> Load kernel from specified partition ---> Mount root partition, start / sbin / init

SysVinit --init reads / etc / inittab ---> /etc/rc[0-6].d/S85httpd etc. ---> Start login process and end

• chkconfig
• update-rc.d
• insserv

systemd --Unit (service / device / mount / swap / target) = processing unit --First, /etc/systemd/system/defalt.target Unit is processed ---> It is a symbolic link to /lib/systemd/system/XX.target --Check running services-> systemctl list-units --type = ○○ --/etc/systemd/system/multi-user.target.wants/Unit configuration files (postfix.service, etc.)

• journalctl -/ var / run / log / journal-> disappears on reboot-> persistent setting in /etc/systemd/jornald.conf

Boot loader

GRUB

• grub-install
• /boot/grub/menu.lst --root (hd0,0)-> / dev / sda1 --Interactive shell-> grub

GRUB2

• grub２-install
• /etc/default/grub -> grub(2)-mkconfig -> /boot/grub/grub.cfg --Interactive shell-> grub2

Startup options ([e] key at startup)

--Specify root file system-> linux /boot/vimlinuz-.4.4.0 ro root = / dec / sda1 --Check boot options-> / proc / cmdline

System recovery

--Start in rescue mode from the installation CD / DVD-ROM --You have to specify the root directory such as rpm command-> Change the root directory with chroot --Modify GRUB configuration file-> grub (2) -mkconfig

Other boot loader

• SYSLINUX --Boot from USB stick or CD-ROM --PXE boot --Network boot
• TFTP/DHCP/HTTP/NFS

4. File system

operation

• /etc/fstab --Check UUID-> blkid --Mount option --noatime-> Do not update inode access time = speed up
• auto
• suid
• user
• users
• defaults -> async/auto/dev/exec/nouser/rw/suid --What filesystems does the kernel support?-> / Proc / filesystems --Which filesystem is mounted-> / etc / mtab = / proc / mounts
• mount / umount --Remount-> mount -o remount / data --sync-> Write the data in the disk buffer area in memory to disk --Procedure to create swap area in file ↓
• dd if=/dev/zero of=/tmp/swapfile bs=1M count=500
• mkswap /tmp/swapfile
• swapon /tmp/swapfile --Check swap space-> swapon -s or cat / proc / swaps

Create

ext

XFS

Btrfs --Checking btrfs usage-> btrfs filesystem df / mnt --Snapshot with btrfs-> btrfs subvolume snapshot A B

CD/DVD

Encrypting file system

Maintenance

--Repair from superblock backup-> ʻe2fsck -b 8193 / dev / sda2`

5. Advanced storage management

RAID

• mdadm --Status-> / proc / mdstat --Settings-> /etc/mdadm.conf
• [_U] --Build RAID-> mdadm --create / dev / md0 --level 5 --raid-devices 3 A B C

LVM

Create

--Partition preparation (parted)-> Physical volume creation (pvcreate)-> Volume group creation (vgcreate)-> Logical volume creation (lvcreate)-> File system creation (mkfs)-> Mount (mount)

Management (reduce / remove attention)

• pvdisplay
• pvscan
• vgextend
• pvmove
• vgreduce
• pvremove
• vgdisplay
• lvdisplay --lvextend-> e2fsck-> resize2fs (for ext filesystem)
• xfs_growfs
• lvremove --Snapshot (lvcreate -s)-> Backup (dump 0uf) --The snapshot area expands when there is a change

Hard disk management

• hdparm(IDE) / sdparm(SATA/SCSI/USB)

SSD --Record in flash memory instead of magnetic disk --When deleting, just flag the data instead of actually erasing it-> Performance degradation-> fstrim -v /

iSCSI

• internet + SCSI --Initiator-> Target

6. Network

• ifconfig
• arp
• ping
• traceroute
• tcpdump
• netstat --netstat -l-> Show only lintening sockets --netstat -i-> Display by interface
• ss
• nc --nc -vz ip address 1-1000-> Port scan in the range 1-1000
• ip [link/addr/route/neigh] [show/add]
• route [add/del]
• iwconfig
• iw dev
• iwlist
• nmcli/nmtui --mtr = my trace route-> operation

7. System maintenance

Install software from source

• patch -p0
• patch -p1 --- R option --Procedure --Obtain and unpack the source code archive (1.tar 2.gunzip; tar 3.gzip -dc | tar) -(Apply if there is a patch file) --Create Makefile with ./configure --Compile with make --Install with sudo make install (all / install / clean) --Located in / usr / local / bin

backup

• type
• Perfect --Differential (can be restored if you have a full backup and the latest differential backup) --Incremental

--Local backup

• tar
• cpio
• dd
• dump/restore --mt-> ex. mt -f / dev / st0 fsf 5-> Fast forward tape from current position to 5 data ahead

--Remote backup

• rsync -auvz --delete -e ssh dir username@hostname:/backupdir

Notification to user

• /etc/motd
• /etc/issue
• /etc/issue.net
• wall

Extra .virtualbox

network

--Set the setting to NAT-> Bridge --ifup interface name --Try to ping