[postgres@pg101 bin]$ postgres: could not find the database system
Expected to find it in the directory "/usr/local/pgsql/bin/../data",
but could not open file "/usr/local/pgsql/bin/../data/global/pg_control": No Such file or Directory

        snprintf(path, sizeof(path), "%s/global/pg_control", DataDir);fp = AllocateFile(path, PG_BINARY_R);if (fp == NULL){write_stderr("%s: could not find the database system\n""Expected to find it in the directory \"%s\",\n""but could not open file \"%s\": %s\n",progname, DataDir, path, strerror(errno));ExitPostmaster(2);}FreeFile(fp);

        /** Set up locale information from environment.  Note that LC_CTYPE and* LC_COLLATE will be overridden later from pg_control if we are in an* already-initialized database.  We set them here so that they will be* available to fill pg_control during initdb.  LC_MESSAGES will get set* later during GUC option processing, but we set it here to allow startup* error messages to be localized.*/set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("postgres"));

/** We maintain an image of pg_control in shared memory.*/
static ControlFileData *ControlFile = NULL;

/** Contents of pg_control.** NOTE: try to keep this under 512 bytes so that it will fit on one physical* sector of typical disk drives.  This reduces the odds of corruption due to* power failure midway through a write.*/typedef struct ControlFileData
{/** Unique system identifier --- to ensure we match up xlog files with the* installation that produced them.*/uint64        system_identifier;/** Version identifier information.    Keep these fields at the same offset,* especially pg_control_version; they won't be real useful if they move* around.    (For historical reasons they must be 8 bytes into the file* rather than immediately at the front.)** pg_control_version identifies the format of pg_control itself.* catalog_version_no identifies the format of the system catalogs.** There are additional version identifiers in individual files; for* example, WAL logs contain per-page magic numbers that can serve as* version cues for the WAL log.*/uint32        pg_control_version;        /* PG_CONTROL_VERSION */uint32        catalog_version_no;        /* see catversion.h *//** System status data*/DBState        state;            /* see enum above */pg_time_t    time;            /* time stamp of last pg_control update */XLogRecPtr    checkPoint;        /* last check point record ptr */XLogRecPtr    prevCheckPoint; /* previous check point record ptr */CheckPoint    checkPointCopy; /* copy of last check point record *//** These two values determine the minimum point we must recover up to* before starting up:** minRecoveryPoint is updated to the latest replayed LSN whenever we* flush a data change during archive recovery. That guards against* starting archive recovery, aborting it, and restarting with an earlier* stop location. If we've already flushed data changes from WAL record X* to disk, we mustn't start up until we reach X again. Zero when not* doing archive recovery.** backupStartPoint is the redo pointer of the backup start checkpoint, if* we are recovering from an online backup and haven't reached the end of* backup yet. It is reset to zero when the end of backup is reached, and* we mustn't start up before that. A boolean would suffice otherwise, but* we use the redo pointer as a cross-check when we see an end-of-backup* record, to make sure the end-of-backup record corresponds the base* backup we're recovering from.*/XLogRecPtr    minRecoveryPoint;XLogRecPtr    backupStartPoint;/** Parameter settings that determine if the WAL can be used for archival* or hot standby.*/int            wal_level;int            MaxConnections;int            max_prepared_xacts;int            max_locks_per_xact;/** This data is used to check for hardware-architecture compatibility of* the database and the backend executable.  We need not check endianness* explicitly, since the pg_control version will surely look wrong to a* machine of different endianness, but we do need to worry about MAXALIGN* and floating-point format.  (Note: storage layout nominally also* depends on SHORTALIGN and INTALIGN, but in practice these are the same* on all architectures of interest.)** Testing just one double value is not a very bulletproof test for* floating-point compatibility, but it will catch most cases.*/uint32        maxAlign;        /* alignment requirement for tuples */double        floatFormat;    /* constant 1234567.0 */
    #define FLOATFORMAT_VALUE    1234567.0/** This data is used to make sure that configuration of this database is* compatible with the backend executable.*/uint32        blcksz;            /* data block size for this DB */uint32        relseg_size;    /* blocks per segment of large relation */uint32        xlog_blcksz;    /* block size within WAL files */uint32        xlog_seg_size;    /* size of each WAL segment */uint32        nameDataLen;    /* catalog name field width */uint32        indexMaxKeys;    /* max number of columns in an index */uint32        toast_max_chunk_size;    /* chunk size in TOAST tables *//* flag indicating internal format of timestamp, interval, time */bool        enableIntTimes; /* int64 storage enabled? *//* flags indicating pass-by-value status of various types */bool        float4ByVal;    /* float4 pass-by-value? */bool        float8ByVal;    /* float8, int8, etc pass-by-value? *//* CRC of all above ... MUST BE LAST! */pg_crc32    crc;
} ControlFileData;