Practical 5. Linux Commands: Working with Files

Transcription

1 Practical 5 Linux Commands: Working with Files 1. Ps The ps command on linux is one of the most basic commands for viewing the processes running on the system. It provides a snapshot of the current processes along with detailed information like user id, cpu usage, memory usage, command name etc. It does not display data in real time like top or htop commands. Ps f : It generates a full listing.

2 Ps a : list information about all processes most frequently requested. Ps A or e : List information for all processes. Ps j : Print session and group ID. 2. Top c top command which is one of the most frequently used commands in our daily system administrative jobs. top command displays processor activity of your Linux box and also displays tasks managed by kernel in real-time. It ll show processor and memory are being used and other information like running processes. This may help you to take correct action. top command found in UNIX-like operating systems. In this example, it will show information like tasks, memory, cpu and swap. Press q or press clt+z to quit window. Top c command will show command line display instead of just command name. 3. Kill Linux Operating System comes with Kill command to terminate a process. The command makes it possible to continue running the server without the need of reboot after a major change/update. Here comes the great power of Linux and this is one of the reasons, why Linux is running on 90% of servers, on the planet. Kill command send a signal, a specified signal to be more perfect to a process. The kill command can be executed in a number of ways, directly or from a shell script. Using kill command from /usr/bin provide you some extra feature to kill a process by process name using pkill. The common syntax for kill command is:

3 # kill [signal or option] PID(s) In order to kill a process, we need to know the Process ID of a process. A Process is an instance of a program. Every-time a program starts, automatically an unique PID is generated for that process. Every Process in Linux, have a pid. For this typr ps command and you can find the process id. For example, we want to kill process with ID 9564 then follow the command: Kill 9564 and press enter. Before we step ahead and execute a kill command, some important points to be noted: 1. A user can kill all his process. 2. A user can not kill another user s process. 3. A user can not kill processes System is using. 4. A root user can kill System-level-process and the process of any user. Pkil : This stands for process killing using their name. For example, you can see that in the below figure one process Mozilla Firefox is currently running and if I want to kill that process use following command: Pkill Mozilla and press enter.

4 Before killing After killing

5 4. Date The date command is used to print out, or change the value of, the system's time and date information. Date command is helpful to display date in several formats. It also allows you to set systems date and time. When you execute date command without any option, it will display the current date and time as shown below. Time

6 Date Format FORMAT is a sequence of characters which specifies how output will appear. It comprises some combination of the following sequences: %a The abbreviated weekday name (e.g., Sun). %A The full weekday name (e.g., Sunday). %b The abbreviated month name (e.g., Jan). %B locale's full month name (e.g., January). 5. Cal Linux also has cal command to display calendar. As its name, cal just show you the calendar in many ways. There is also ncal command which have same function with cal. Cal is a built-in command which shipped in every Linux distribution. To run cal, just type cal on your console. Display calendar in full year view To display it in full year view, put the year you want to view after cal command or use -y year parameter. Let s say you want to view 2013 calendar. Simply type the below commands:

7 cal 2013 or cal -y 2013 Show specific month To fulfill this, we can use -m month_name parameter. Here s a sample: cal -m Feb Print Julian days Julian days is days one-based which numbered from January 1. To print calendar in this format, use -j parameter. cal -j

8 On Julian calender, we see that December 7, 2013 is converted into day 341 in 2013 year. Display 3 months calender You can display calender in 3 month format. One for previous, current and next month. Use - 3parameter to do it. cal -3 Display the number of month after the current month If you need to do it, use -A number parameter. cal -A 2

9 Display the number of month before the current month If you need to do it, use -B number parameter. cal -B 2 Print week numbers To show a week number, we can not use cal command. This time, we use ncal command. ncal w Ncal print a portrait view. The week numbers are printed on the bottom of each months. Weeks start on Monday By default, weeks start on Sunday. If you want to start on Monday, you can use -M parameter. Once again, this parameter is applied to ncal command only. ncal -M

10 Display country codes To print country codes in calendar, we can use -p parameter. This parameter also only applied to ncal command. ncal p 6. Uptime uptime tells you how long the system has been running. uptime gives a one-line display of the following information: The current time how long the system has been running how many users are currently logged on the system load averages for the past 1, 5, and 15 minutes. This is the same information contained in the header line displayed by w. System load averages is the average number of processes that are either in a runnable or uninterruptable state. A process in a runnable state is either using the CPU or waiting to use the CPU. A process in uninterruptable state is waiting for some I/O access, eg waiting for disk. The averages are taken over the three time intervals. Load averages are not normalized for the number of CPUs in a system, so a load average of 1 means a single CPU system is loaded all the time while on a 4 CPU system it means it was idle75% of the time.

11 7. W The w command display who is logged into the Linux and Unix-like server, and what they are doing at command execution time. w displays information about the users currently on the machine, and their processes. The header of the the output shows (in this order): the current time, how long the system has been running, how many users are currently logged on, and the system load averages for the past 1, 5, and 15 minutes. The following entries are displayed for each user: login name, the tty name, the remote host they are logged in from, the amount of time they have been logged in, their idle time, JCPU, PCPU, and the command line of their current process. The JCPU time is the time used by all processes attached to the tty. It does not include past background jobs, but does include currently running background jobs. The PCPU time is the time used by the current process, named in the "what" field.

12 8. Whoami whoami prints the effective user ID. This command prints the username associated with the current effective user ID. Running whoami is the same as running the id command with the options -un. whoami syntax whoami [OPTION] Options --help --version Display a help message, and exit. Display version information, and exit.

13 9. Uname This command prints the name of current operating system.

14 Kernel name To reveal the kernel name, you can use -s parameter. uname s o/p: Linux The output will be same with uname without parameter. Kernel release If you need to know what kernel release you re using, just use -r parameter uname r o/p: el5 Kernel version Beside kernel information, uname can also fetch the kernel version. Use -v parameter for this purpose uname v o/p: 1 SMP Tue Oct 22 12:57:43 EDT 2013 Nodename Parameter -n will give you the node hostname. For example, if your hostname is devmachine, -n parameter will print dev-machine as the output of -n parameter uname n o/p: dev-machine Hardware name If you are wondering what kind of machine you re using, you can try -m parameter. It will show you information about it. uname m o/p: i686

15 i686 is indicates that your system is 32 bit operating system. While x86_64 means your system is a 64 bit system. Hardware platform Similar with hardware name, -i parameter will show you hardware platfrom. uname i o/p: i386 i386 mean you are running a 32 bit system. If the output is x86_64 it s mean that you are running 64 bis system. Processor type To see processor type, you can use -p parameter. If uname is not able to show you that information, it will show you unknown in the output. uname p o/p: i686 Operating system Uname can also used to reveal what operating system you are running. Use -o parameter to fulfill this purpose. uname o o/p: GNU/Linux All information There is one parameter that can reveal all information. It s -a parameter. It will show you all information except omit -i and -p if they are unknown. uname a o/p: Linux dev-machine el5 #1 SMP Tue Oct 22 12:57:43 EDT 2013 i686 i686 i386 GNU/Linux

16 10. Man On Linux and other Unix-like operating systems, man is the interface used to view the system's reference manuals. man is the system's manual viewer; it can be used to display manual pages, scroll up and down, search for occurrences of specific text, and other useful functions. Each argument given to man is normally the name of a program, utility or function. The manual page associated with each of these arguments is then found and displayed. A section number, if provided, will direct man to look only in that section of the manual. The default action is to search in all of the available sections, following a pre-defined order and to show only the first page found, even if page exists in several sections. For example, if we want to view about mkdir command: Man mkdir and press enter, you can see the following output. 11. Df The 'df' command stand for disk filesystem, it is used to get full summary of available and used disk space usage of file system on Linux system. Using '-h' parameter with (df -h) will shows the file system disk space statistics in human readable format, means it gives the details in bytes, megabytes and gigabyte.

17 Check File System Disk Space Usage The df command displays the information of device name, total blocks, total disk space, used disk space, available disk space and mount points on a file system. [root@tecmint ~]# df Filesystem 1K-blocks Used Available Use% Mounted on /dev/cciss/c0d0p % / /dev/cciss/c0d0p % /home /dev/cciss/c0d0p % /data /dev/cciss/c0d0p % /boot tmpfs % /dev/shm Display Information of all File System Disk Space Usage The same as above, but it also displays information of dummy file systems along with all the file system disk usage and their memory utilization. [root@tecmint ~]# df -a Filesystem 1K-blocks Used Available Use% Mounted on /dev/cciss/c0d0p % / proc /proc sysfs /sys devpts /dev/pts /dev/cciss/c0d0p % /home /dev/cciss/c0d0p % /data /dev/cciss/c0d0p % /boot tmpfs % /dev/shm none /proc/sys/fs/binfmt_misc sunrpc /var/lib/nfs/rpc_pipefs Show Disk Space Usage in Human Readable Format Have you noticed that above commands displays information in bytes, which is not readable yet all, because we are in a habit of reading the sizes in megabytes, gigabytes etc. as it makes very easy to understand and remember. The df command provides an option to display sizes in Human Readable formats by using -h (prints the results in human readable format (e.g., 1K 2M 3G)).

18 ~]# df -h Filesystem Size Used Avail Use% Mounted on /dev/cciss/c0d0p2 75G 23G 49G 32% / /dev/cciss/c0d0p5 24G 22G 1.2G 95% /home /dev/cciss/c0d0p3 29G 25G 2.6G 91% /data /dev/cciss/c0d0p1 289M 22M 253M 8% /boot tmpfs 252M 0 252M 0% /dev/shm Display Information of File System in Bytes To display all file system information and usage in 1024-byte blocks, use the option -k (e.g. block-size=1k) as follows. [root@tecmint ~]# df -k Filesystem 1K-blocks Used Available Use% Mounted on /dev/cciss/c0d0p % / /dev/cciss/c0d0p % /home /dev/cciss/c0d0p % /data /dev/cciss/c0d0p % /boot tmpfs % /dev/shm Display Information of File System in MB To display information of all file system usage in MB (Mega Byte) use the option as -m. [root@tecmint ~]# df -m Filesystem 1M-blocks Used Available Use% Mounted on /dev/cciss/c0d0p % / /dev/cciss/c0d0p % /home /dev/cciss/c0d0p % /data /dev/cciss/c0d0p % /boot tmpfs % /dev/shm Display Information of File System in GB To display information of all file system statistics in GB (Gigabyte) use the option as df -h. [root@tecmint ~]# df -h Filesystem Size Used Avail Use% Mounted on /dev/cciss/c0d0p2 75G 23G 49G 32% /

19 /dev/cciss/c0d0p5 24G 22G 1.2G 95% /home /dev/cciss/c0d0p3 29G 25G 2.6G 91% /data /dev/cciss/c0d0p1 289M 22M 253M 8% /boot tmpfs 252M 0 252M 0% /dev/shm Display File System Inodes Using -i switch will display the information of number of used inodes and their percentage for the file system. [root@tecmint ~]# df -i Filesystem Inodes IUsed IFree IUse% Mounted on /dev/cciss/c0d0p % / /dev/cciss/c0d0p % /home /dev/cciss/c0d0p % /data /dev/cciss/c0d0p % /boot tmpfs % /dev/shm Display File System Type If you notice all the above commands output, you will see there is no file system type mentioned in the results. To check the file system type of your system use the option T. It will display file system type along with other information. [root@tecmint ~]# df -T Filesystem Type 1K-blocks Used Available Use% Mounted on /dev/cciss/c0d0p2 ext % / /dev/cciss/c0d0p5 ext % /home /dev/cciss/c0d0p3 ext % /data /dev/cciss/c0d0p1 ext % /boot tmpfs tmpfs % /dev/shm Display Information of df Command. Using help switch will display a list of available option that are used with df command. [root@tecmint ~]# df --help Usage: df [OPTION]... [FILE]... Show information about the file system on which each FILE resides, or all file systems by default.

20 Mandatory arguments to long options are mandatory for short options too. -a, --all include dummy file systems -B, --block-size=size use SIZE-byte blocks -h, --human-readable print sizes in human readable format (e.g., 1K 234M 2G) -H, --si likewise, but use powers of 1000 not i, --inodes list inode information instead of block usage -k like --block-size=1k -l, --local limit listing to local file systems --no-sync do not invoke sync before getting usage info (default) -P, --portability use the POSIX output format --sync invoke sync before getting usage info -t, --type=type limit listing to file systems of type TYPE -T, --print-type print file system type -x, --exclude-type=type limit listing to file systems not of type TYPE -v (ignored) --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. Report bugs to <bug-coreutils@gnu.org>. 12. Du

21 The Linux du (Disk Usage) is a standard Unix/Linux command, used to check the information of disk usage of files and directories on a machine. The du command has many parameter options that can be used to get the results in many formats. The du command also displays the files and directory sizes in a recursively manner. Du a : Displays the usage of space that each file is taking up. Du s : report total sum for each of the specified files.

22 Du-h : prints in human readable format. 13. Free

23 The most important and single way of determining the total available space of the physical memory and swap memory is by using free command. The Linux free command gives information about total used and available space of physical memory and swap memory with buffers used by kernel in Linux/Unix like operating systems. Display Memory in Bytes Free command with option -b, display the size of memory in Bytes. # free -b total used free shared buffers cached Mem: /+ buffers/cache: Swap: Display Memory in Kilo Bytes Free command with option -k, display the size of memory in (KB) Kilobytes. # free -k total used free shared buffers cached Mem:

24 -/+ buffers/cache: Swap: Display Memory in Megabytes To see the size of the memory in (MB) Megabytes use option as -m. # free -m total used free shared buffers cached Mem: /+ buffers/cache: Swap: Display Memory in Gigabytes Using -g option with free command, would display the size of the memory in GB(Gigabytes). # free -g total used free shared buffers cached Mem: /+ buffers/cache: 0 0 Swap: Display Total Line Free command with -t option, will list the total line at the end. # free -t total used free shared buffers cached Mem: /+ buffers/cache: Swap: Total: Disable Display of Buffer Adjusted Line By default the free command display buffer adjusted line, to disable this line use option as -o.

25 # free -o total used free shared buffers cached Mem: Swap: Dispaly Memory Status for Regular Intervals The -s option with number, used to update free command at regular intervals. For example, the below command will update free command every 5 seconds. # free -s 5 total used free shared buffers cached Mem: /+ buffers/cache: Swap: Show Low and High Memory Statistics The -l switch displays detailed high and low memory size statistics. # free -l total used free shared buffers cached Mem: Low: High: /+ buffers/cache: Swap: Check Free Version The -V option, display free command version information. # free -V procps version Whereis Locates the binary, source, and manual page files for a command. whereis locates source/binary and manuals sections for specified files. The supplied names are first stripped of

26 leading pathname components and any (single) trailing extension of the form ".ext", for example, ".c". Prefixes of "s." resulting from use of source code control are also handled. whereis then attempts to locate the desired program in a list of standard Linux places.