CentOS knowledge point summary

1. crontab (1) execute */bin/date & gt;/tmp/date.txt * sleep10 every 10 seconds; /bin/date & gt;/tmp/date.txt (2) 1. crontab (1) crontab is executed every 10 seconds

*/Bin/date>/tmp/date.txt * sleep 10;/bin/date>/tmp/date.txt

(2) You can also use the following methods to express

String meaning
-------------
@ Reboot Run once, at startup.
@ Yearly Run once a year, "0 0 1 *".
@ Annually (same as @ yearly)
@ Monthly Run once a month, "0 0 1 **".
@ Weekly Run once a week, "0 0 ** 0 ".
@ Daily Run once a day, "0 0 ***".
@ Midnight (same as @ daily)
@ Hourly Run once an hour, "0 ****".

2. kick the user offline

Root @ iZ94hgp4s2xZ :~ # W 10:15:27 up 1 day, 19: 20, 2 users, load average: 0.00, 0.01, 0.05 user tty from login @ idle jcpu pcpu what jediael pts/0 31.00 s 0.13 s 0.13 s-bash root pts/1 218.107.55.252 15 1.00 s 0.02 s 0.00 s w root @ iZ94hgp4s2xZ: ~ # Pkill-kill-t pts/0

3. several bin directories/bin: Commands related to boot, including system repairs in single-user mode, such as cp mv bash dmsg grep chmod/sbin: Same as above, generally, root is allowed to use commands such as init iptables lvm/usr/bin: commands unrelated to startup: java tail gcc/usr/sbin: Same as above, generally, the root command useradd usermod/usr/local/bin: when the same software requires a different version but does not want to delete the original version, install the new software here/user/local/sbin: Same as above, general commands used by root 4. view the memory and cpu information in the proc file system cat/proc/cpuinfo cat/proc/meminfo 5. some common commands and options

Cat/etc/passwd | cut-D': '-f 1 apt-cache dumpavail | grep 'package: mysql 'cat/etc/passwd | sort-t ': '-k 3-n last | cut-d''-f 1 | sort | uniq-c

6. basic steps for disk partitioning (1) create a partition fdisk (2) format the partition mkfs (3) Check the disk and fsck (4) mount the disk. 7. common commands for apt (1) install apt-get install scala (2) specify a certain version of apt-get install calla = 2.9.2 (3) delete a software apt-get remove scala (4) find a software apt-cache search scala