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       --sparse=WHEN

              control creation of sparse files. See below

        By default, sparse SOURCE files are detected by a crude heuristic and the corresponding DEST file is made sparse as well.  That is the behavior selected by --sparse=auto.  Specify --sparse=always to create a sparse DEST file whenever the SOURCE file contains a long enough sequence of zero bytes.  Use --sparse=never to inhibit creation of sparse files.

       -S, --sparse

              Handle sparse files efficiently.  Some files in the file system may have segments which were actually never written (quite often these are database files created by such systems as DBM).  When given this option, tar attempts to determine if the file is sparse prior to archiving it, and if so, to reduce the resulting archive size by not dumping empty parts of the file. 

$ tar -cvfS test_spar.tar 123123.qcow2

$ tar -S -cvf test_spar.tar 123123.qcow2 

$ ll

-rw-------. 1 root root   9665380352 Aug  8  2018 123123.qcow2

-rw-r--r--. 1 root root      1484800 Feb 14 18:10 test_spar.tar

-rw-r--r--. 1 root root   9665382400 Feb 14 18:09 test.tar

 To have tar attempt to recognize the holes in a file, use `--sparse' (`-S'). 

Advantages

The advantage of sparse files is that storage is only allocated when actually needed: disk space is saved, and large files can be created even if there is insufficient free space on the file system.

Disadvantages

Disadvantages are that sparse files may become fragmented; file system free space reports may be misleading; filling up file systems containing sparse files can have unexpected effects; and copying a sparse file with a program that does not explicitly support them may copy the entire, uncompressed size of the file, including the sparse, mostly zero sections which are not on disk -- losing the benefits of the sparse property in the file. 

ls -s tells you the allocated size of the file, always a multiple of the allocation unit. ls -l tells the actual size. An easy way to test: 

$ man ls

       --block-size=SIZE

              scale sizes by SIZE before printing them; e.g., '--block-size=M'

              prints sizes in units of 1,048,576 bytes; see SIZE format below 

# setsebool samba_export_all_rw 1 

[root@localhost ~]# getsebool -a | grep samba

samba_create_home_dirs --> off

samba_domain_controller --> off

samba_enable_home_dirs --> off

samba_export_all_ro --> off

samba_export_all_rw --> off

samba_load_libgfapi --> off

samba_portmapper --> off

samba_run_unconfined --> off

samba_share_fusefs --> off

samba_share_nfs --> off

sanlock_use_samba --> off

tmpreaper_use_samba --> off

use_samba_home_dirs --> off

virt_use_samba --> off

[root@localhost ~]# getsebool -a | grep smb

smbd_anon_write --> off

[root@localhost ~]# getsebool -a | grep nmb

[root@localhost ~]# 

If you want to allow samba to share any file/directory read/write, you must turn on the samba_export_all_rw boolean.

setsebool -P samba_export_all_rw 1 

(1) TCP_HIT, TCP_MEM_HIT

    요청한 컨텐츠가 캐시에 있어서 응답한 경우

(2) TCP_MISS

    요청한 컨텐츠가 캐시에 없어서 실제 서버로 요청을 하여 응답한 경우

    대부분 이미지 외 것에 해당한다.

(3) TCP_IMS_HIT

    클라이언트가 If-Modified-Since 필드를 요청 헤더에 보냈는데 HIT가 났다는 의미이다. 

    만약 결과 HTTP코드값이 '304 Not Modified'로 나왔다면 캐시는

    클라이언트로 컨텐츠를 보낼 필요없이 클라이언트 브라우저에 있는 컨텐츠를 사용한다는 의미이다.

(4) TCP_IMS_MISS 

    요청헤더에 If-Modified-Since 가 포함되어 있지만 캐시가 신선하지 않다고 판단되어 실제 서버로 재요청을 한 경우

(5) TCP_REFRESH_HIT 

    요청한 컨텐츠가 신선하지 않아 실제 서버로 요청했는데 '304 Not Modified'를 받아 캐시에서 클라이언트로 응답한 경우

(6) TCP_REFRESH_MISS 

    요청한 컨텐츠가 신선하지 않아 실제 서버로 요청했는데 

    서버에서 새로운 컨텐츠를 전송받아 캐시에 저장하고 다시 클라이언트로 응답

(7) TCP_CLIENT_REFRESH 

    클라이언트 요청 헤더에 'no_cache'를 포함한 경우

(8) TCP_CLIENT_REFRESH_MISS 

    클라이언트 요청에 'no-cache'나 'no-store'같은 캐시를 제어하는 필드를 포함하여서 

    캐시가 서버로부터 컨텐츠를 가져왔을때

(9) TCP_DENIED 

    클라이언트 요청이 캐시에 의해서 거절당했을 경우(컨텐츠필터링과 연관) 

* Matched If-None-Match requests are logged as TCP_INM_HIT (proposed by Amos)

* If-Modified-Since requests for modified cached objects are processed as normal HITs

* Not matched If-None-Match requests for cached objects are processed as normal HITs

* If-Modified-Since header is ignored if If-None-Match header exists (RFC7232 compliance)