/etc/localtime

/etc/localtime configures the system-wide timezone of the local system. It may be link to /usr/share/zoneinfo/ followed by a timezone identifier such as "Europe/Berlin" or "Etc/UTC" pointing to binary tzfile(5) timezone data for the configured timezone.

from mac os 12

ls -l /usr/share/zoneinfo/ 
lrwxr-xr-x  1 root  wheel  38 Aug 27 16:58 /usr/share/zoneinfo/@ -> /var/db/timezone/tz/2022c.1.0/zoneinfo

+VERSION    (2022c)

PST8PDT     MST  MST7MDT CST6CDT     EST EST5EDT     HST(Hawaii) W-SU(Washington State University)
iso3166.tab
Universal   Factory     leapseconds posixrules  zone.tab

Cuba        Egypt       GB          Eire(Ireland) GB-Eire   Hongkong    Iceland     Iran   Israel      Jamaica     Japan       
Libya       Navajo(MT)  NZ          NZ-CHAT(islands)     
Portugal    Poland      PRC(China)  ROC    ROK(RepublicOfKorea)    Singapore   Turkey      Kwajalein(island)       
            
WET(Western European)   CET(Centeral European) == MET(Middle European)   EET(Eastern European)   

Australia/  Brazil/     Chile/      Indian/  Mexico/        US/     
America/    Canada/     Atlantic/   Pacific/    
Europe/     Africa/     /Antarctica/ Arctic/     Asia/       


Etc/
GMT  == GMT0 == GMT-0 == GMT+0   == Zulu    Greenwich  Universal
UCT == UTC
GMT+1       GMT+2       GMT+3       GMT+4       GMT+5       GMT+6       GMT+7       GMT+8       GMT+9       
GMT+10      GMT+11      GMT+12      

GMT-1       GMT-2       GMT-3       GMT-4       GMT-5       GMT-6       GMT-7       GMT-8       GMT-9       
GMT-10      GMT-11      GMT-12      GMT-13      GMT-14      

hexdump -C GMT
00  54 5a 69 66 32 00 00 00  00 00 00 00 00 00 00 00  |TZif2
10  00 00 00 00 00 00 00 01  00 00 00 01 00 00 00 00
20  00 00 00 00 00 00 00 01  00 00 00 04 00 00 00 00 
30  00 00 47 4d 54 00 00 00                           |GMT

30                           54 5a 69 66 32 00 00 00  |   TZif2|
40  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 01 
50  00 00 00 01 00 00 00 00  00 00 00 00 00 00 00 01  
60  00 00 00 04 00 00 00 00  00 00 47 4d 54 00 00 00  |    GMT   |
70  0a 47 4d 54 30 0a                                 | GMT0 |

> Zulu
TZif2 UTC
TZif2 UTC UTC0.

> Greenwich 
TZif2 GMT
TZif2 GMT GMT0.

> GMT-1
00  54 5a 69 66 32 00 00 00  00 00 00 00 00 00 00 00  |TZif2

30  00 00 2b 30 31 00 00 00                           |..+01
30                           54 5a 69 66 32 00 00 00  |        TZif2

60  00 00 00 04 00 00 0e 10  00 00 2b 30 31 00 00 00  |          +01
70  0a 3c 2b 30 31 3e 2d 31  0a                       |.<+01>-1.|




Timezone identifier is extracted from the target name of /etc/localtime

The timezone may be overridden for individual programs by using $TZ . See environ(7).

timedatectl(1) changes this file during runtime.
systemd-firstboot(1) to initialize the time zone on mounted (but not booted) system images.

-rw-r--r-- 1 root root 3519 Nov  5 14:00 localtime
 >hexdump -C localtime

000  54 5a 69 66 32 00 00 00  00 00 00 00 00 00 00 00  |TZif2           |
010  00 00 00 00 00 00 00 04  00 00 00 04 00 00 00 00  
020  00 00 00 eb 00 00 00 04  00 00 00 10 9e a6 1e 70  
030  9f ba eb 60 a0 86 00 70  a1 9a cd 60 a2 65 e2 70  
040  a3 83 e9 e0 a4 6a ae 70  a5 35 a7 60 a6 53 ca f0  
050  a7 15 89 60 a8 33 ac f0  a8 fe a5 e0 aa 13 8e f0  
060  aa de 87 e0 ab f3 70 f0  ac be 69 e0 ad d3 52 f0  
070  ae 9e 4b e0 af b3 34 f0  b0 7e 2d e0 b1 9c 51 70  
080  b2 67 4a 60 b3 7c 33 70  b4 47 2c 60 b5 5c 15 70  
090  b6 27 0e 60 b7 3b f7 70  b8 06 f0 60 b9 1b d9 70  
0a0  b9 e6 d2 60 bb 04 f5 f0  bb c6 b4 60 bc e4 d7 f0  
0b0  bd af d0 e0 be c4 b9 f0  bf 8f b2 e0 c0 a4 9b f0  
0c0  c1 6f 94 e0 c2 84 7d f0  c3 4f 76 e0 c4 64 5f f0  
0d0  c5 2f 58 e0 c6 4d 7c 70  c7 0f 3a e0 c8 2d 5e 70  
0e0  c8 f8 57 60 ca 0d 40 70  ca d8 39 60 cb 88 f0 70  
0f0  d2 23 f4 70 d2 60 fb e0  d3 75 e4 f0 d4 40 dd e0  
100  d5 55 c6 f0 d6 20 bf e0  d7 35 a8 f0 d8 00 a1 e0  
110  d9 15 8a f0 d9 e0 83 e0  da fe a7 70 db c0 65 e0  
120  dc de 89 70 dd a9 82 60  de be 6b 70 df 89 64 60  
130  e0 9e 4d 70 e1 69 46 60  e2 7e 2f 70 e3 49 28 60  
140  e4 5e 11 70 e5 57 2e e0  e6 47 2d f0 e7 37 10 e0  
150  e8 27 0f f0 e9 16 f2 e0  ea 06 f1 f0 ea f6 d4 e0  
160  eb e6 d3 f0 ec d6 b6 e0  ed c6 b5 f0 ee bf d3 60  
170  ef af d2 70 f0 9f b5 60  f1 8f b4 70 f2 7f 97 60  
180  f3 6f 96 70 f4 5f 79 60  f5 4f 78 70 f6 3f 5b 60  
190  f7 2f 5a 70 f8 28 77 e0  f9 0f 3c 70 fa 08 59 e0  
1a0  fa f8 58 f0 fb e8 3b e0  fc d8 3a f0 fd c8 1d e0  
1b0  fe b8 1c f0 ff a7 ff e0  00 97 fe f0 01 87 e1 e0  
1c0  02 77 e0 f0 03 70 fe 60  04 60 fd 70 05 50 e0 60  
1d0  06 40 df 70 07 30 c2 60  07 8d 19 70 09 10 a4 60  
1e0  09 ad 94 f0 0a f0 86 60  0b e0 85 70 0c d9 a2 e0  
1f0  0d c0 67 70 0e b9 84 e0  0f a9 83 f0 10 99 66 e0  
200  11 89 65 f0 12 79 48 e0  13 69 47 f0 14 59 2a e0  
210  15 49 29 f0 16 39 0c e0  17 29 0b f0 18 22 29 60  
220  19 08 ed f0 1a 02 0b 60  1a f2 0a 70 1b e1 ed 60  
230  1c d1 ec 70 1d c1 cf 60  1e b1 ce 70 1f a1 b1 60  
240  20 76 00 f0 21 81 93 60  22 55 e2 f0 23 6a af e0  
250  24 35 c4 f0 25 4a 91 e0  26 15 a6 f0 27 2a 73 e0  
260  27 fe c3 70 29 0a 55 e0  29 de a5 70 2a ea 37 e0  
270  2b be 87 70 2c d3 54 60  2d 9e 69 70 2e b3 36 60  
280  2f 7e 4b 70 30 93 18 60  31 67 67 f0 32 72 fa 60  
290  33 47 49 f0 34 52 dc 60  35 27 2b f0 36 32 be 60  
2a0  37 07 0d f0 38 1b da e0  38 e6 ef f0 39 fb bc e0  
2b0  3a c6 d1 f0 3b db 9e e0  3c af ee 70 3d bb 80 e0  
2c0  3e 8f d0 70 3f 9b 62 e0  40 6f b2 70 41 84 7f 60  
2d0  42 4f 94 70 43 64 61 60  44 2f 76 70 45 44 43 60  
2e0  45 f3 a8 f0 47 2d 5f e0  47 d3 8a f0 49 0d 41 e0  
2f0  49 b3 6c f0 4a ed 23 e0  4b 9c 89 70 4c d6 40 60  
300  4d 7c 6b 70 4e b6 22 60  4f 5c 4d 70 50 96 04 60  
310  51 3c 2f 70 52 75 e6 60  53 1c 11 70 54 55 c8 60  
320  54 fb f3 70 56 35 aa 60  56 e5 0f f0 58 1e c6 e0  
330  58 c4 f1 f0 59 fe a8 e0  5a a4 d3 f0 5b de 8a e0  
340  5c 84 b5 f0 5d be 6c e0  5e 64 97 f0 5f 9e 4e e0  
350  60 4d b4 70 61 87 6b 60  62 2d 96 70 63 67 4d 60  
360  64 0d 78 70 65 47 2f 60  65 ed 5a 70 67 27 11 60  
370  67 cd 3c 70 69 06 f3 60  69 ad 1e 70 6a e6 d5 60  
380  6b 96 3a f0 6c cf f1 e0  6d 76 1c f0 6e af d3 e0  
390  6f 55 fe f0 70 8f b5 e0  71 35 e0 f0 72 6f 97 e0  
3a0  73 15 c2 f0 74 4f 79 e0  74 fe df 70 76 38 96 60  
3b0  76 de c1 70 78 18 78 60  78 be a3 70 79 f8 5a 60  
3c0  7a 9e 85 70 7b d8 3c 60  7c 7e 67 70 7d b8 1e 60  
3d0  7e 5e 49 70 7f 98 00 60  00 01 00 01 00 01 00 01  
3e0  00 01 00 01 00 01 00 01  00 01 00 01 00 01 00 01  
*
400  00 01 00 01 00 01 00 01  02 03 01 00 01 00 01 00  
410  01 00 01 00 01 00 01 00  01 00 01 00 01 00 01 00  |                |
*
4c0  01 00 01 ff ff c7 c0 01  00 ff ff b9 b0 00 04 ff  |                |
4d0  ff c7 c0 01 08 ff ff c7  c0 01 0c 45 44 54 00 45  |           EDT E|
4e0  53 54 00 45 57 54 00 45  50 54 00 00 00 00 01 00  |ST EWT EPT      |

4f0  00 00 01 54 5a 69 66 32  00 00 00 00 00 00 00 00  |   TZif2        |
500  00 00 00 00 00 00 00 00  00 00 05 00 00 00 05 00  
510  00 00 00 00 00 00 ec 00  00 00 05 00 00 00 14 ff  
520  ff ff ff 5e 03 f0 90 ff  ff ff ff 9e a6 1e 70 ff  
530  ff ff ff 9f ba eb 60 ff  ff ff ff a0 86 00 70 ff  
540  ff ff ff a1 9a cd 60 ff  ff ff ff a2 65 e2 70 ff  
550  ff ff ff a3 83 e9 e0 ff  ff ff ff a4 6a ae 70 ff  
560  ff ff ff a5 35 a7 60 ff  ff ff ff a6 53 ca f0 ff  
570  ff ff ff a7 15 89 60 ff  ff ff ff a8 33 ac f0 ff  
580  ff ff ff a8 fe a5 e0 ff  ff ff ff aa 13 8e f0 ff  
590  ff ff ff aa de 87 e0 ff  ff ff ff ab f3 70 f0 ff  
5a0  ff ff ff ac be 69 e0 ff  ff ff ff ad d3 52 f0 ff  
5b0  ff ff ff ae 9e 4b e0 ff  ff ff ff af b3 34 f0 ff  
5c0  ff ff ff b0 7e 2d e0 ff  ff ff ff b1 9c 51 70 ff  
5d0  ff ff ff b2 67 4a 60 ff  ff ff ff b3 7c 33 70 ff  
5e0  ff ff ff b4 47 2c 60 ff  ff ff ff b5 5c 15 70 ff  
5f0  ff ff ff b6 27 0e 60 ff  ff ff ff b7 3b f7 70 ff  
600  ff ff ff b8 06 f0 60 ff  ff ff ff b9 1b d9 70 ff  
610  ff ff ff b9 e6 d2 60 ff  ff ff ff bb 04 f5 f0 ff  
620  ff ff ff bb c6 b4 60 ff  ff ff ff bc e4 d7 f0 ff  
630  ff ff ff bd af d0 e0 ff  ff ff ff be c4 b9 f0 ff  
640  ff ff ff bf 8f b2 e0 ff  ff ff ff c0 a4 9b f0 ff  
650  ff ff ff c1 6f 94 e0 ff  ff ff ff c2 84 7d f0 ff  
660  ff ff ff c3 4f 76 e0 ff  ff ff ff c4 64 5f f0 ff  
670  ff ff ff c5 2f 58 e0 ff  ff ff ff c6 4d 7c 70 ff  
680  ff ff ff c7 0f 3a e0 ff  ff ff ff c8 2d 5e 70 ff  
690  ff ff ff c8 f8 57 60 ff  ff ff ff ca 0d 40 70 ff  
6a0  ff ff ff ca d8 39 60 ff  ff ff ff cb 88 f0 70 ff  
6b0  ff ff ff d2 23 f4 70 ff  ff ff ff d2 60 fb e0 ff  
6c0  ff ff ff d3 75 e4 f0 ff  ff ff ff d4 40 dd e0 ff  
6d0  ff ff ff d5 55 c6 f0 ff  ff ff ff d6 20 bf e0 ff  
6e0  ff ff ff d7 35 a8 f0 ff  ff ff ff d8 00 a1 e0 ff  
6f0  ff ff ff d9 15 8a f0 ff  ff ff ff d9 e0 83 e0 ff  
700  ff ff ff da fe a7 70 ff  ff ff ff db c0 65 e0 ff  
710  ff ff ff dc de 89 70 ff  ff ff ff dd a9 82 60 ff  
720  ff ff ff de be 6b 70 ff  ff ff ff df 89 64 60 ff  
730  ff ff ff e0 9e 4d 70 ff  ff ff ff e1 69 46 60 ff  
740  ff ff ff e2 7e 2f 70 ff  ff ff ff e3 49 28 60 ff  
750  ff ff ff e4 5e 11 70 ff  ff ff ff e5 57 2e e0 ff  
760  ff ff ff e6 47 2d f0 ff  ff ff ff e7 37 10 e0 ff  
770  ff ff ff e8 27 0f f0 ff  ff ff ff e9 16 f2 e0 ff  
780  ff ff ff ea 06 f1 f0 ff  ff ff ff ea f6 d4 e0 ff  
790  ff ff ff eb e6 d3 f0 ff  ff ff ff ec d6 b6 e0 ff  
7a0  ff ff ff ed c6 b5 f0 ff  ff ff ff ee bf d3 60 ff  
7b0  ff ff ff ef af d2 70 ff  ff ff ff f0 9f b5 60 ff  
7c0  ff ff ff f1 8f b4 70 ff  ff ff ff f2 7f 97 60 ff  
7d0  ff ff ff f3 6f 96 70 ff  ff ff ff f4 5f 79 60 ff  
7e0  ff ff ff f5 4f 78 70 ff  ff ff ff f6 3f 5b 60 ff  
7f0  ff ff ff f7 2f 5a 70 ff  ff ff ff f8 28 77 e0 ff  
800  ff ff ff f9 0f 3c 70 ff  ff ff ff fa 08 59 e0 ff  
810  ff ff ff fa f8 58 f0 ff  ff ff ff fb e8 3b e0 ff  
820  ff ff ff fc d8 3a f0 ff  ff ff ff fd c8 1d e0 ff  
830  ff ff ff fe b8 1c f0 ff  ff ff ff ff a7 ff e0 00  
840  00 00 00 00 97 fe f0 00  00 00 00 01 87 e1 e0 00  
850  00 00 00 02 77 e0 f0 00  00 00 00 03 70 fe 60 00  
860  00 00 00 04 60 fd 70 00  00 00 00 05 50 e0 60 00  
870  00 00 00 06 40 df 70 00  00 00 00 07 30 c2 60 00  
880  00 00 00 07 8d 19 70 00  00 00 00 09 10 a4 60 00  
890  00 00 00 09 ad 94 f0 00  00 00 00 0a f0 86 60 00  
8a0  00 00 00 0b e0 85 70 00  00 00 00 0c d9 a2 e0 00  
8b0  00 00 00 0d c0 67 70 00  00 00 00 0e b9 84 e0 00  
8c0  00 00 00 0f a9 83 f0 00  00 00 00 10 99 66 e0 00  
8d0  00 00 00 11 89 65 f0 00  00 00 00 12 79 48 e0 00  
8e0  00 00 00 13 69 47 f0 00  00 00 00 14 59 2a e0 00  
8f0  00 00 00 15 49 29 f0 00  00 00 00 16 39 0c e0 00  
900  00 00 00 17 29 0b f0 00  00 00 00 18 22 29 60 00  
910  00 00 00 19 08 ed f0 00  00 00 00 1a 02 0b 60 00  
920  00 00 00 1a f2 0a 70 00  00 00 00 1b e1 ed 60 00  
930  00 00 00 1c d1 ec 70 00  00 00 00 1d c1 cf 60 00  
940  00 00 00 1e b1 ce 70 00  00 00 00 1f a1 b1 60 00  
950  00 00 00 20 76 00 f0 00  00 00 00 21 81 93 60 00  
960  00 00 00 22 55 e2 f0 00  00 00 00 23 6a af e0 00  
970  00 00 00 24 35 c4 f0 00  00 00 00 25 4a 91 e0 00  
980  00 00 00 26 15 a6 f0 00  00 00 00 27 2a 73 e0 00  
990  00 00 00 27 fe c3 70 00  00 00 00 29 0a 55 e0 00  
9a0  00 00 00 29 de a5 70 00  00 00 00 2a ea 37 e0 00  
9b0  00 00 00 2b be 87 70 00  00 00 00 2c d3 54 60 00  
9c0  00 00 00 2d 9e 69 70 00  00 00 00 2e b3 36 60 00  
9d0  00 00 00 2f 7e 4b 70 00  00 00 00 30 93 18 60 00  
9e0  00 00 00 31 67 67 f0 00  00 00 00 32 72 fa 60 00  
9f0  00 00 00 33 47 49 f0 00  00 00 00 34 52 dc 60 00  
a00  00 00 00 35 27 2b f0 00  00 00 00 36 32 be 60 00  
a10  00 00 00 37 07 0d f0 00  00 00 00 38 1b da e0 00  
a20  00 00 00 38 e6 ef f0 00  00 00 00 39 fb bc e0 00  
a30  00 00 00 3a c6 d1 f0 00  00 00 00 3b db 9e e0 00  
a40  00 00 00 3c af ee 70 00  00 00 00 3d bb 80 e0 00  
a50  00 00 00 3e 8f d0 70 00  00 00 00 3f 9b 62 e0 00  
a60  00 00 00 40 6f b2 70 00  00 00 00 41 84 7f 60 00  
a70  00 00 00 42 4f 94 70 00  00 00 00 43 64 61 60 00  
a80  00 00 00 44 2f 76 70 00  00 00 00 45 44 43 60 00  
a90  00 00 00 45 f3 a8 f0 00  00 00 00 47 2d 5f e0 00  
aa0  00 00 00 47 d3 8a f0 00  00 00 00 49 0d 41 e0 00  
ab0  00 00 00 49 b3 6c f0 00  00 00 00 4a ed 23 e0 00  
ac0  00 00 00 4b 9c 89 70 00  00 00 00 4c d6 40 60 00  
ad0  00 00 00 4d 7c 6b 70 00  00 00 00 4e b6 22 60 00  
ae0  00 00 00 4f 5c 4d 70 00  00 00 00 50 96 04 60 00  
af0  00 00 00 51 3c 2f 70 00  00 00 00 52 75 e6 60 00  
b00  00 00 00 53 1c 11 70 00  00 00 00 54 55 c8 60 00  
b10  00 00 00 54 fb f3 70 00  00 00 00 56 35 aa 60 00  
b20  00 00 00 56 e5 0f f0 00  00 00 00 58 1e c6 e0 00  
b30  00 00 00 58 c4 f1 f0 00  00 00 00 59 fe a8 e0 00  
b40  00 00 00 5a a4 d3 f0 00  00 00 00 5b de 8a e0 00  
b50  00 00 00 5c 84 b5 f0 00  00 00 00 5d be 6c e0 00  
b60  00 00 00 5e 64 97 f0 00  00 00 00 5f 9e 4e e0 00  
b70  00 00 00 60 4d b4 70 00  00 00 00 61 87 6b 60 00  
b80  00 00 00 62 2d 96 70 00  00 00 00 63 67 4d 60 00  
b90  00 00 00 64 0d 78 70 00  00 00 00 65 47 2f 60 00  
ba0  00 00 00 65 ed 5a 70 00  00 00 00 67 27 11 60 00  
bb0  00 00 00 67 cd 3c 70 00  00 00 00 69 06 f3 60 00  
bc0  00 00 00 69 ad 1e 70 00  00 00 00 6a e6 d5 60 00  
bd0  00 00 00 6b 96 3a f0 00  00 00 00 6c cf f1 e0 00  
be0  00 00 00 6d 76 1c f0 00  00 00 00 6e af d3 e0 00  
bf0  00 00 00 6f 55 fe f0 00  00 00 00 70 8f b5 e0 00  
c00  00 00 00 71 35 e0 f0 00  00 00 00 72 6f 97 e0 00  
c10  00 00 00 73 15 c2 f0 00  00 00 00 74 4f 79 e0 00  
c20  00 00 00 74 fe df 70 00  00 00 00 76 38 96 60 00  
c30  00 00 00 76 de c1 70 00  00 00 00 78 18 78 60 00  
c40  00 00 00 78 be a3 70 00  00 00 00 79 f8 5a 60 00  
c50  00 00 00 7a 9e 85 70 00  00 00 00 7b d8 3c 60 00  
c60  00 00 00 7c 7e 67 70 00  00 00 00 7d b8 1e 60 00  
c70  00 00 00 7e 5e 49 70 00  00 00 00 7f 98 00 60 02  
c80  01 02 01 02 01 02 01 02  01 02 01 02 01 02 01 02  
*
cb0  03 04 02 01 02 01 02 01  02 01 02 01 02 01 02 01  
cc0  02 01 02 01 02 01 02 01  02 01 02 01 02 01 02 01  
*
d60  02 01 02 01 02 01 02 01  02 01 02 ff ff ba 9e 00  
d70  00 ff ff c7 c0 01 04 ff  ff b9 b0 00 08 ff ff c7  

d80  c0 01 0c ff ff c7 c0 01  10 4c 4d 54 00 45 44 54  |         LMT EDT|
d90  00 45 53 54 00 45 57 54  00 45 50 54 00 00 00 00  | EST EWT EPT    |
da0  00 01 00 00 00 00 01 0a  45 53 54 35 45 44 54 2c  |        EST5EDT,|
db0  4d 33 2e 32 2e 30 2c 4d  31 31 2e 31 2e 30 0a     |M3 2 0,M11 1 0 |