Here I am going to review some useful Linux commands. As we are Java programmer and JDK is compatible in most platforms and since most of server platforms are Linux base, so we should know how to work with them. there are some common commands which we need them like copy, cut, remove, service stop, show processes and so on.
I am not going to teach Linux and Linux core. Here I prepare you as a simple user of Linux.
OK let's start:
Note: You can use --help in front of any following command to display help of the specified command. But some practical switches will be available here.
Example: ls --help
Result:
Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor --sort.
Mandatory arguments to long options are mandatory for short options too.
-a, --all do not ignore entries starting with .
-A, --almost-all do not list implied . and ..
--author with -l, print the author of each file
-b, --escape print octal escapes for nongraphic characters
--block-size=SIZE use SIZE-byte blocks
-B, --ignore-backups do not list implied entries ending with ~
-c with -lt: sort by, and show, ctime (time of last
modification of file status information)
with -l: show ctime and sort by name
otherwise: sort by ctime
-C list entries by columns
--color[=WHEN] control whether color is used to distinguish file
types. WHEN may be `never', `always', or `auto'
-d, --directory list directory entries instead of contents,
and do not dereference symbolic links
-D, --dired generate output designed for Emacs' dired mode
-f do not sort, enable -aU, disable -lst
-F, --classify append indicator (one of */=>@|) to entries
--file-type likewise, except do not append `*'
--format=WORD across -x, commas -m, horizontal -x, long -l,
single-column -1, verbose -l, vertical -C
--full-time like -l --time-style=full-iso
-g like -l, but do not list owner
-G, --no-group like -l, but do not list group
-h, --human-readable with -l, print sizes in human readable format
(e.g., 1K 234M 2G)
--si likewise, but use powers of 1000 not 1024
-H, --dereference-command-line
follow symbolic links listed on the command line
--dereference-command-line-symlink-to-dir
follow each command line symbolic link
that points to a directory
--hide=PATTERN do not list implied entries matching shell PATTERN
(overridden by -a or -A)
--indicator-style=WORD append indicator with style WORD to entry names:
none (default), slash (-p),
file-type (--file-type), classify (-F)
-i, --inode with -l, print the index number of each file
-I, --ignore=PATTERN do not list implied entries matching shell PATTERN
-k like --block-size=1K
-l use a long listing format
-L, --dereference when showing file information for a symbolic
link, show information for the file the link
references rather than for the link itself
-m fill width with a comma separated list of entries
-n, --numeric-uid-gid like -l, but list numeric user and group IDs
-N, --literal print raw entry names (don't treat e.g. control
characters specially)
-o like -l, but do not list group information
-p, --indicator-style=slash
append / indicator to directories
-q, --hide-control-chars print ? instead of non graphic characters
--show-control-chars show non graphic characters as-is (default
unless program is `ls' and output is a terminal)
-Q, --quote-name enclose entry names in double quotes
--quoting-style=WORD use quoting style WORD for entry names:
literal, locale, shell, shell-always, c, escape
-r, --reverse reverse order while sorting
-R, --recursive list subdirectories recursively
-s, --size with -l, print size of each file, in blocks
-S sort by file size
--sort=WORD extension -X, none -U, size -S, time -t,
version -v, status -c, time -t, atime -u,
access -u, use -u
--time=WORD with -l, show time as WORD instead of modification
time: atime, access, use, ctime or status; use
specified time as sort key if --sort=time
--time-style=STYLE with -l, show times using style STYLE:
full-iso, long-iso, iso, locale, +FORMAT.
FORMAT is interpreted like `date'; if FORMAT is
FORMAT1<newline>FORMAT2, FORMAT1 applies to
non-recent files and FORMAT2 to recent files;
if STYLE is prefixed with `posix-', STYLE
takes effect only outside the POSIX locale
-t sort by modification time
-T, --tabsize=COLS assume tab stops at each COLS instead of 8
-u with -lt: sort by, and show, access time
with -l: show access time and sort by name
otherwise: sort by access time
-U do not sort; list entries in directory order.
In combination with one_per_line format `-1',
it will show files immediately and it has no
memory limitations.
-v sort by version
-w, --width=COLS assume screen width instead of current value
-x list entries by lines instead of by columns
-X sort alphabetically by entry extension
-1 list one file per line
SELinux options:
--lcontext Display security context. Enable -l. Lines
will probably be too wide for most displays.
-Z, --context Display security context so it fits on most
displays. Displays only mode, user, group,
security context and file name.
--scontext Display only security context and file name.
--help display this help and exit
--version output version information and exit
SIZE may be (or may be an integer optionally followed by) one of following:
kB 1000, K 1024, MB 1000*1000, M 1024*1024, and so on for G, T, P, E, Z, Y.
By default, color is not used to distinguish types of files. That is
equivalent to using --color=none. Using the --color option without the
optional WHEN argument is equivalent to using --color=always. With
--color=auto, color codes are output only if standard output is connected
to a terminal (tty). The environment variable LS_COLORS can influence the
colors, and can be set easily by the dircolors command.
Exit status is 0 if OK, 1 if minor problems, 2 if serious trouble.
Report bugs to <bug-coreutils@gnu.org>.
- pwd: To show the current directory where you are in. you can use this command any where.
Example: [root@testserver ~]# pwd
Result: /root - clear: To clear the screen.
Example: [root@testserver ~]# clear
Result: [root@testserver ~]# - cd: To change the current directory to specified directory.
- cd /: return to the root path
- cd ..: return to the upper directory
- cd .: return to the current directory
Result: [root@testserver data]# - ls: To list the directory content.
- ls -list: lists the directory content in detail like creation time, size and so on.
- ls -f: does not sort.
- ls | grep a: lists the directory content containing 'a' in their name
- cp source destination: To copy source to destination.
Example: [root@testserver opt]# cp test.cnf /root/test.cnf
Result: copies test.cnf from current directory(/opt) to /root directory - cp -r source destination: To copy source directory to destination.
Example: [root@testserver opt]# cp -r data /root/data2
Result: copies data folder to /root directory in new name (data2) - mv source destination: To cut(move) source to destination. you can also use it to rename a directory or file.
Example: [root@testserver opt]# mv data data2
Result: renames data directory to data2 - rm filename: To remove file with specified filename
Example: [root@testserver opt]# rm /root/test.cnf
Result: removes test.cnf in /root path - rm -rf directoryname: To remove directory and all containing files and sub-directories recursively(r) without prompting(f)
Example: [root@testserver opt]# rm -rf /root/data2
Result: remove data2 directory and all its containing data from /root path - ps aux: To list the running system processes in detail like cpu usage, memory usage, process id and so on.
Example: [root@testserver opt]# ps aux
Result:USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 0.0 10348 548 ? Ss Jan11 0:01 init [5]
root 2 0.0 0.0 0 0 ? S< Jan11 0:00 [migration/0]
root 3 0.0 0.0 0 0 ? SN Jan11 0:00 [ksoftirqd/0]
root 4 0.0 0.0 0 0 ? S< Jan11 0:00 [watchdog/0]
root 5 0.0 0.0 0 0 ? S< Jan11 0:00 [migration/1]
root 6 0.0 0.0 0 0 ? SN Jan11 0:00 [ksoftirqd/1]
root 7 0.0 0.0 0 0 ? S< Jan11 0:00 [watchdog/1]
root 8 0.0 0.0 0 0 ? S< Jan11 0:00 [migration/2]
root 9 0.0 0.0 0 0 ? SN Jan11 0:00 [ksoftirqd/2]
... -
ps aux | grep somthing: To Filter the list of processes to specified name. It searches in processes detail and variables by specified name and show you in details.
Example: [root@testserver opt]# ps aux | grep tomcat
Result:root 5593 0.0 9.3 1460380 370892 ? Sl Feb19 3:38 /opt/jdk1.6.0_07/bin/java -Djava.util.logging.config.file=/opt/apache-tomcat-6.0.18/conf/logging.properties -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -Xms256m -Xmx1024m -XX:MaxPermSize=256m -Djava.endorsed.dirs=/opt/apache-tomcat-6.0.18/endorsed -classpath /opt/apache-tomcat-6.0.18/bin/bootstrap.jar -Dcatalina.base=/opt/apache-tomcat-6.0.18 -Dcatalina.home=/opt/apache-tomcat-6.0.18 -Djava.io.tmpdir=/opt/apache-tomcat-6.0.18/temp org.apache.catalina.startup.Bootstrap start
root 22672 0.0 0.0 61180 744 pts/5 S+ 12:04 0:00 grep tomcat
- kill -9 PID: To kill the process with specified PID. you can find PID by ps command then use this command to kill it.
Note: PID is not fix for processes. A new PID will be assign any time you run some process so you should first catch it by ps command.
Example: [root@testserver opt]# kill -9 5593
Result: kills process with id of 5593(tomcat process) - unzip zipfilename: To unzip the zipped file.
Example: [root@testserver opt]# unzip test.zip
Result: unzips the test.zip file. - execute a process: you should just write the executive file with its path then press enter to start it. if you want to start it in background of the shell put '&' sign in front of the file name
Example: [root@testserver bin]# ./catalina.sh run &
Result: executes catalina.sh in back ground with run switch(the needed parameter of this file). if you don't specify '&' sign it shows you in the current shell and you will not able to write a new command. so you should first stop it. In this state (running the process in current shell) press Ctrl + c to stop it. But if you run it in background, you should kill this process to stop it. - service --status-all: To list the current services and their status.
Example: [root@testserver opt]# service --status-all
Result:acpid (pid 2410) is running...
anacron is stopped
atd (pid 2627) is running...
auditd (pid 2138) is running...
automount (pid 2476) is running...
Avahi daemon is running
Avahi DNS daemon is not running
hcid (pid 2330) is running...
sdpd (pid 2336) is running...
capi not installed - No such file or directory (2)
conmand is stopped
cpuspeed is stopped
crond (pid 2581) is running...
cupsd (pid 2520) is running...
cups-config-daemon is obsolete
dnsmasq is stopped
dund is stopped
Usage: /etc/init.d/firstboot {start|stop}
gpm (pid 2572) is running...
hald (pid 2419) is running...
hidd (pid 2453) is running...
hpiod (pid 2493) is running...
hpssd (pid 2498) is running...
Firewall is stopped.
ipmi_msghandler module not loaded.
ipmi_si module not loaded.
ipmi_devintf module not loaded.
/dev/ipmi0 does not exist.
Firewall is stopped.
irattach is stopped
irqbalance (pid 2220) is running...
Kdump is not operational
krb524d is stopped
mcstransd (pid 1904) is running...
mdadm is stopped
mdmpd is stopped
dbus-daemon (pid 2308) is running...
multipathd is stopped
mysqld (pid 21367) is running...
netconsole module not loaded
netplugd is stopped
Configured devices:
lo eth0
Currently active devices:
lo eth0
NetworkManager is stopped
rpc.mountd is stopped
nfsd is stopped
rpc.rquotad is stopped
rpc.statd (pid 2269) is running...
nscd is stopped
ntpd is stopped
pand is stopped
pcscd (pid 2400) is running...
portmap (pid 2231) is running...
Process accounting is disabled.
rdisc is stopped
restorecond (pid 2157) is running...
rpc.idmapd (pid 2293) is running...
saslauthd is stopped
sendmail (pid 2553) is running...
setroubleshootd (pid 2320) is running...
smartd (pid 2719) is running...
openssh-daemon (pid 2511) is running...
syslogd (pid 2166) is running...
klogd (pid 2169) is running...
Xvnc is stopped
wdaemon is stopped
winbindd is stopped
wpa_supplicant is stopped
xfs (pid 2610) is running...
xinetd (pid 2534) is running...
ypbind is stopped
yum-updatesd (pid 2850) is running... -
service servicename [stop|start|restart]: To stop or start or restart the service with specified service name.
Example: [root@testserver opt]# service mysqld restart
Result:Stopping MySQL: [ OK ]
Starting MySQL: [ OK ] - vi filename: To edit or even create (if not exist) a file content. It opens the specified file in editor. you can first view it. but if you are going to change it, press Insert key on your keyboard then you can change it. after changing:
- Esc then ":w" then Enter: will save the file.
- Esc then ":q" then Enter: will quit the editor.
- Esc then ":wq" then Enter: will save the file and quit the editor.
- Esc then ":q!" then Enter: will quit editor without saving the file.
- free: To show memory status like total size, free space and so on.
Example: [root@testserver opt]# free
Result:total used free shared buffers cached
Mem: 3979020 3642384 336636 0 256836 1167672
-/+ buffers/cache: 2217876 1761144
Swap: 6029304 382832 5646472 -
df: To show the discs and their status.
Example: [root@testserver opt]# df
Result:Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
230601592 7762296 210936320 4% /
/dev/sda1 101086 12508 83359 14% /boot
tmpfs 1989508 0 1989508 0% /dev/shm - chmod -R MOD directory|file: To define permissions for specified directory or file. if you want to assign the permission to all containing files and sub-directory of the specified directory, you should use -R else it is not necessary. MOD is a 3 or 4 digits. every digits has it own meaning. Take a look the following gadget. click any box and see the result. the result will be the MOD.
Result:R W X Owner Group Others - export variableName="value": to define a variable with specified name and value.
Example: [root@testserver opt]# export test="/opt/data"
Result: test variable will be created. - echo $variableName: to show variable value.
Example: [root@testserver opt]# echo $test
Result: /opt/data
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