From the kernel version you have posted, it seems you are running Oracle Linux 6 and you should download the Red Hat Enterprise Linux 6 / Oracle Linux 6 version instead of version 7 as you tried now.

So, the following commands should work for you.

yum remove mysql57-community-release.noarch
yum clean all
yum install
yum install mysql-community-server

# sudo grep “temporary password” /var/log/mysqld.log


ALTER USER ‘root’@’localhost’ IDENTIFIED BY ‘password’;

2018-03-07T08:32:28.128407Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use –explicit_defaults_for_timestamp server option (see documentation for more details).
2018-03-07T08:32:29.274779Z 0 [Warning] InnoDB: New log files created, LSN=45790
2018-03-07T08:32:29.457933Z 0 [Warning] InnoDB: Creating foreign key constraint system tables.
2018-03-07T08:32:29.518358Z 0 [Warning] No existing UUID has been found, so we assume that this is the first time that this server has been started. Generating a new UUID: 12b823f8-21e2-11e8-90e9-fa163e03a800.
2018-03-07T08:32:29.520280Z 0 [Warning] Gtid table is not ready to be used. Table ‘mysql.gtid_executed’ cannot be opened.
2018-03-07T08:32:29.520904Z 1 [Note] A temporary password is generated for root@localhost: rte/nA*Cl1Q=
2018-03-07T08:32:36.582974Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use –explicit_defaults_for_timestamp server option (see documentation for more details).
2018-03-07T08:32:36.585295Z 0 [Note] /usr/sbin/mysqld (mysqld 5.7.21) starting as process 16937 …
2018-03-07T08:32:36.589311Z 0 [Note] InnoDB: PUNCH HOLE support available
2018-03-07T08:32:36.589330Z 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2018-03-07T08:32:36.589336Z 0 [Note] InnoDB: Uses event mutexes
2018-03-07T08:32:36.589348Z 0 [Note] InnoDB: GCC builtin __sync_synchronize() is used for memory barrier
2018-03-07T08:32:36.589352Z 0 [Note] InnoDB: Compressed tables use zlib 1.2.3
2018-03-07T08:32:36.589356Z 0 [Note] InnoDB: Using Linux native AIO
2018-03-07T08:32:36.589623Z 0 [Note] InnoDB: Number of pools: 1
2018-03-07T08:32:36.589735Z 0 [Note] InnoDB: Using CPU crc32 instructions
2018-03-07T08:32:36.591356Z 0 [Note] InnoDB: Initializing buffer pool, total size = 128M, instances = 1, chunk size = 128M
2018-03-07T08:32:36.600783Z 0 [Note] InnoDB: Completed initialization of buffer pool
2018-03-07T08:32:36.603371Z 0 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority().
2018-03-07T08:32:36.615611Z 0 [Note] InnoDB: Highest supported file format is Barracuda.
2018-03-07T08:32:36.641547Z 0 [Note] InnoDB: Creating shared tablespace for temporary tables
2018-03-07T08:32:36.641596Z 0 [Note] InnoDB: Setting file ‘./ibtmp1’ size to 12 MB. Physically writing the file full; Please wait …
2018-03-07T08:32:36.740907Z 0 [Note] InnoDB: File ‘./ibtmp1’ size is now 12 MB.
2018-03-07T08:32:36.741821Z 0 [Note] InnoDB: 96 redo rollback segment(s) found. 96 redo rollback segment(s) are active.
2018-03-07T08:32:36.741831Z 0 [Note] InnoDB: 32 non-redo rollback segment(s) are active.
2018-03-07T08:32:36.743082Z 0 [Note] InnoDB: Waiting for purge to start
2018-03-07T08:32:36.793329Z 0 [Note] InnoDB: 5.7.21 started; log sequence number 2551549
2018-03-07T08:32:36.794305Z 0 [Note] InnoDB: Loading buffer pool(s) from /var/lib/mysql/ib_buffer_pool
2018-03-07T08:32:36.794528Z 0 [Note] Plugin ‘FEDERATED’ is disabled.
2018-03-07T08:32:36.796246Z 0 [Note] InnoDB: Buffer pool(s) load completed at 180307 3:32:36
2018-03-07T08:32:36.801164Z 0 [Note] Found ca.pem, server-cert.pem and server-key.pem in data directory. Trying to enable SSL support using them.
2018-03-07T08:32:36.801403Z 0 [Warning] CA certificate ca.pem is self signed.
2018-03-07T08:32:36.802831Z 0 [Note] Server hostname (bind-address): ‘*’; port: 3306
2018-03-07T08:32:36.802866Z 0 [Note] IPv6 is available.
2018-03-07T08:32:36.802874Z 0 [Note] – ‘::’ resolves to ‘::’;
2018-03-07T08:32:36.802894Z 0 [Note] Server socket created on IP: ‘::’.
2018-03-07T08:32:36.812651Z 0 [Note] Event Scheduler: Loaded 0 events
2018-03-07T08:32:36.812823Z 0 [Note] /usr/sbin/mysqld: ready for connections.
Version: ‘5.7.21’ socket: ‘/var/lib/mysql/mysql.sock’ port: 3306 MySQL Community Server (GPL)
2018-03-07T08:32:37.215231Z 2 [Note] Access denied for user ‘UNKNOWN_MYSQL_USER’@’localhost’ (using password: NO)
2018-03-07T08:32:47.687315Z 3 [Note] Access denied for user ‘root’@’localhost’ (using password: NO)